OP, this is very circumstantial proof in my opinion but I think enough to flag him as a fishy character.

My primary concern with PryptoMontreal is that how he is able to get his OneVanilla gift cards at more than a 35% discount. This generally suggests that the method he obtains these gift cards (if he actually has them) is shady at best, or illegal at worst.

These are warning signs already. I haven't seen any legit gift card sellers that obtain their cards in legitimate ways offer such steep discounts.

If you were to deal with this guy, understand that even escrow won't protect you from a fraudulently obtained card. Escrow only protects the transaction process itself.