had quick scan and only really seen Artificer based enquires, so sorry if its a repeat.

So my curiosity is does the Cantrip Tattoo get a power boost based on level. As a lot get a boost based on character level from how I read cantrips, take eldritch blast...

"At Higher Levels. The spell creates more than one beam when you reach higher levels: two beams at 5th level, three beams at 11th level, and four beams at 17th level. You can direct the beams at the same target or at different ones. Make a separate attack roll for each beam."

So potentially adds more power to the Tattoo than I first considered. Although equally if a character attempted to craft, or infuse, would we consider the current level of the crafter towards this rather than the level of the user. User level I imagine is easier to track, although crafter level could add more flavour... "Character gets a tattoo charged with Eldritch blast, They are at level 11. Expecting 3 beams to fire only to find a singular beam fizzes across the battlefield as they got a better price from the merchant to take the apprentice's craftwork. Could even potentially use such an event to hint that something strange is occurring at the merchants, to find they are using child labour to manufacture magic items. On the other hand, could amplify the power where the product was made by a Takumi master. Allowing DM to flavour up the one shot, and potentially flip an encounter from TPK to a close encounter, although perhaps a party that resorts to a cantrip tattoo for an emergency damage option should be taught with that TPK. Although only takes one boosted power Tattoo to suddenly get the party willing to invest

My other curiosity is are the spells limited to there spell levels. Rarer Tattoos get better modifiers, along with some spells getting additional power when cast at higher levels. So could you get a Fire Ball in a level 5 Tattoo, so would have an additional 2d6 as 2 levels above level 3 and would get better saving throw DC. Considering this with the crafting aspect again, getting them to roll and then on a Natural 20 having a means to boost it's potential. 

RAW  from the DMG Magic Item Rules:
"Some magic items allow the user to cast a spell from the item, often by expending charges from it. The spell is cast at the lowest possible spell and caster level, doesn’t expend any of the user’s spell slots, and requires no components unless the item’s description says otherwise."

So, a cantrip would be cast at level 1.

Theoretically, you could store a 5th level Fireball in the highest level Spellwraught Tattoo, at least I'd consider that rules legal.

Cantrips are not upcast.  Instead their power level depends upon your total character level. 

All cantrips are cast at level 0 and the effect goes up as you level up. If you cast a cantrip and are level 17, you get the level 17 effect - whether you are using a tattoo or anything else.

My mistake, as proven by others here.  Ignore this post.

"The spell is cast at the lowest possible spell and caster level" so also lowest caster level, which is level 1 for cantrips.

Thank you Voras.

Would you consider the level of the Tattoo with cantrip. May seem wasteful to put a cantrip in a higher Tattoo although If I was to consider the scaling up of other spells then it too would require a passing thought. but on that bases would we need to consider the lowest level to unlock that size spell slot. and apply modifiers on that bases.

Might still run an exception if the players agree to allow cantrips within tattoos to be level effected through the producer. If nothing else it should encourage them to RP more with traders 

This was pretty much my thinking as well,  Voras did well to see the little details.

Although I wonder when we consider crafting vs pre existing magic items whether the same rules truly applies. Although that's where we end up with the debate if RAW and RAI. 

Which at end of the day comes down to what works with the current group and adds the most enjoyed flavour to a game. If offer something which adds extra power(or could hinder it) then need to add something equally that challenges it. 

Idea of shop bought or found 1 shot ideas being able to be amplified in a moment of crisis or restricted in a moment over overpower gives a fast fix to a "I'd not balanced this encounter properly" moment. With an easy story explained reason to balance it out works nicely. Although may only be a once shot recover as the team then learn there are variations which could be investigated