"Well that was fast, seems convenient. How can i be sure you did the deed and not just playing prank on me?" 

/anyone with an argument or proof or both provided can attempt Persuasion roll. If you present both (proof and argument) roll with advantage/

Progo starts to walks back and forth by the doors. "Well thanks to your super insightful information, we were able to best determine a way of discovering the creature. With your helpful subjects, we were able to swiftly canvas the rooms. Then managed to get the creature to reveal itself. Unfortunately it did so by trying to eat Progo. Progo's clothed still bear the scars and stains of the unveiling. Progo's now full of monster teeth and acid marks. But as it turns out, a creature with the ability to form itself into any mundane object, doesn't leave much behind when dispatched. We have a handful of it's liquid-like remains. The rest, we'll you may want to buy a real rug to cover that mess."

Persuasion: 10

"I would add two thing, if you may Progo. First, is that you can ask your guards, they must have heard the fight. They were only 30-50 ft away."

He then grab his amulet of Bahamut and shows it to the Kings "Secondly, I am a servant of Bahamut - The Justice Bringer - and I would not do petty lies for a rewards.". "I do not lies about my deeds.." he continues with a most serious face.

Persuasion: 25 (natural 20 !)

"That is great news ! Truly Marvelous, come closer to the door let me see that goo of a monster remains!" He opens the doors only little bit to see trough the gap and exclaims. "Yes that must be it! It stinks the same as that murderous rug! Thank you oh thank you oh brave travelers for aiding my kingdom. Wait just a second and let me thank you properly" You hear rapid footsteps going away from the doors. After couple moments King yells: "Come in travelers King will see you know." Upon entrance you see two thrones on which Korboz And Gnerkli sits, there is lose rope lying by the Gnerkli Throne. Korboz says: "Gnomegarde thanks you for your aid brave travelers you vanquished the monster who was terrorizing our territory. As a token of gratitude i wish to gift you this hat of wizardry. This is a useful kind of a hat and i hope it will help you in your endeavors." then Gnerkli stands up and says: "I am really grateful for your presence here in Gnomegared at this troubling moment. I really don't know how would i be able to withstand this /and makes a subtle but not so subtle short stare at Korboz/ Anyway my gift can't compare to what you already been given but still please accept this wand of pyrotechnics from me as a thank you." Korboz is speaking again: "Bit don't think that conlcudes our bussines. I am giving you one time access to our vault, and each one of you can take one item from there. Please fetch me Fibblestib Dabbledob, to open the vault for you."

« Many thanks King Korboz.. these gift might help against a potential dragon attack ». Gorse th looks at the two magical items and talk to his group of friend « these two things  are probably for you, I don’t see myself wearing this hat. Let’s go check the vault then ! »

When Fibblestib and Dabbledob open the vault, you see before you a pile of junk. Big pile of junk, but as you remember, Tryncaryn did saw magic in this room, so there should be something of use.

/Everyone please roll an investigation roll to see who found what/

If there is time to do that, Tryn will be recasting Detect Magic as a ritual, otherwise he’ll cast it normal with a slot.

Investigation: 6

Progo investigation: 8

sure you can cast it as ritual, the overall time of searching trough that gigantic pile of scrap would close to an hour for everyone to find something, but with detect magic you find those with ease  clockwork amulet and a pole of collapsing. as for others i will post the findings later.

Goraseth investigates : 9

Tryncaryn informs the others about his finding, “Look what I found! That could be useful. Let’s make a stack of useful things and then decide together what each on of us takes. We can each only take one item as far as I understand.”

(Are they identified and we know what they do? Or perhaps the gnomes would tell us?)

Tharanau looks through the pile of useless stuff. His thoughts are still with this king. He seemed very feeble and useless. He also did see the side glance and wondered a bit more about the dynamics of power inside this gnomengarde 

Tharanau investigation 21 (character sheet)

Yes, the gnomes gladly tell you about any item you find. For investigations rolls:

Tryncaryn finds - lock

Progo finds - alchemist fire (flask), antitoxin (vial)

Goraseth finds - Lantern, bullseye

Tharanau finds - Poison, basic (vial)

That is correct one person can leave with one item from the vault. The rummaging took you about an hour and it is about 4 pm right now.

I am on mobile right now at work, will edit to hyperlinks once I'm home.

Goraseth's eyes land on a beautiful lantern shape as a dragon "beautiful and useful" he thought to himself.
He turns to the two gnomes accompagnying them "my friends, the night is almost upon is, would you mind if we stay here for the night ?"

Tryn chooses the clockwork amulet and leaves to pole for anyone that isn’t happy with their find. “The pole could be useful and it is transportable, but poison and alchemists fire isn’t bad either, albeit the latter two we could probably buy in Phandalin.” Then he agrees with Seth, “It would be nice indeed if we could stay here, we would like to continue on this trek and it would be a pity if we have to return late to town only to have to leave earlier tomorrow.”

(Progo wants to get into being a potion seller and maker, so I think he will go for the alchemist's fire. I think the pole woukd be a much better choice though. Also we have other collections to make, like the spell book and items to help the town)

“Yeah, I was wondering if we could convince the gnome at the front door, the one with the crossbow machine, to come with us to Phandalin and install something similar there. A defense system against a dragon attack. The people of Phandalin would be forever indebted to the ingenious gnomes of Gnomengarde,” Tryn comments to Fibblestib and Dabbledob. “What was her name again? Factore?”

"We sure think it can be arranged, and it will be our pleasure. However we do not have a place for guest as we usually do not have any, but i hope it would not be too weird if we prepare a place to sleep for you in the chamber with barrels where you slayed the monster. We will clean up the place and place something comfortable to lay on for you. In the time being you are invited to the feast, where you can taste our food and fill your bellies before sleep."

"Ah and considering Factore... hmm... no we can not allow that. Factore is not exactly fully wat you call it... sane. Having her outside of known space might spark many unwanted behaviors. Not to mention your clash with that most certainly didn't put you in her grace. We had many hard times with her before we got to some kind of understating for her needs and how to live peacefully with her where all of us including her can live and be content about your lives. Now she is resting and i insist that you would not encounter here for her and yours sake."

/who had not yet stated what they picked from vault, should still do it/

For supper you are led to the dining room, which comes with some difficulties for medium sized folks as the furniture is a little to small. You are served with made mostly of green spongy bread accompanied with stew of vegetables and little bit of game meat. To drink you are being given purple wine that distinctive taste of mushrooms. The taste is not great, not bad either, but an acquired taste for sure. Later you are shown to your sleeping area. A makeshift beds out of hay and sheets are prepared in barrel room for you to spend the night. 

/Between supper and sleep you would still have around 2 or 3 hours of free time so feel free to state what you do or roleplay in gnomegarde/

Before going to bed, Goraseth goes to talk with the engineers gnome. "May I say that the idea of Tryn is, I think, excellent. The crossbow weapon is very powerful, my ribs still hurt when breath. It could have an effect on the dragon. I understand that Factore is in no place to come to Phandalin, but could we borrow the blueprints of this machine. We have very clever compagnon that could maybe build one in the village."
He waits , a bit and to help his case, he continues: " Can you imagine if the weapon from Gnomegarde saves us, or even better kills the beast !!! You would be famous, and I know a bit about being famous. I am sure the mayor would pay a good amount of gold, but I am sure that renown is a far better currency."

"I understand the pressure you feel when you have safety of the village and all arounds on you shoulder against a dragon. I know it is hard on you. I wish i could help with that. Factore does not do blueprint, all is in her beautiful twisted mind. We can not extract that. And none of us is capable of creating such monstrosities. You see most of us have some knack for fiddling with gears, and sometimes we create something functional but most of the times it is a streak of failures that eventually lead not even to success but at least a good lesson."