Map prices are insane, and you're putting the control of them on players (who can either be biased or way too greedy). If the one hard to get one even IS available only one single person can get it, which leaves the other 600 or whatever with pretty much no chance of ever getting it. And yeah, I know, goals aren't supposed to be easy, but they're not simply difficult, they're practically impossible.
Always willing to help! Forced to buy from my shop for a quest? See me later and I will refund your MP in exchange for an equitable trade. Willing to swap photos/plates for ANY value for ones I don't have.