The time you've spent painstakingly working fabrics into breathtaking ensembles has given you an acute awareness of even the most miniscule of outfit detailing. By examining materials that can justifiably be used in tailoring, you can determine precisely what kind of material you're looking at, and even assess it's quality compared to other examples of the same material. Even the most convincing of knock-offs will have a hard time passing as the genuine article when subjected to your trained gaze. Discuss with your DM what qualifies as a "material that can justifiably be used in tailoring". This may be limited solely to fabrics, or, if your DM decides you have sufficient experience incorporating metals or gems into your work (a royal tailor used to making fine clothes for nobles might fit this description), they might allow this benefit to apply to metals and/or gems that were particularly common in your works.

You have a reliable and trustworthy contact within the fashion business who can help keep you connected to the various goings-on of the greater fashion world. Their help can range from information on what trends are currently in vogue and where to get the best materials for the best price, to arranging meetings with other members of the fashion community. Work with your DM to determine how this contact is connected to the fashion world, as their exact role in it may influence the kind of help they can best provide. If they are a textile manufacturer, perhaps they can provide insight on magical versions of mundane materials that they produce. If they are a promoter, perhaps they can advise you on how best to convey information to a desired audience. If they are a favored personal tailor to a local noble, they may even be able to put in a good enough word to convince the noble to hold an audience with you and your party.