Did dark ages King’s ever know for sure any certain Christian religious relics were inauthentic and yet still displayed and sold access too? Are there any sources proving this, Evidence to support it happening?

There's always more to be said on this matter, so if anyone reading this thread has a contribution, feel free to go right ahead! While we wait for those, OP, you may be interested in this previous question regarding Medieval relics and the authenticity thereof, ably answered by u/WelfOnTheShelf.