First of all, I believe that ALL magical items, or those possessing any supernatural abilities and traits, should be so valuable and rare that literally no one would sell them, no matter how much coin anyone offers. To be blunt, I am completely for the idea of 99% shops selling purely "mundane" items, those produced through regular labour and other technological means. The only "magical" items which could be sold on a more or less regular basis, but still be extremely expensive, would be potions.
Secondly, no "Identify" spell should be available, thus opening the possibility for a character to buy, for a hefty sum, a "blessed relic" from a priest in a temple, which later on turns out to be nothing more than a regular devotional item. I have no qualms about simply punishing the players for being too carefree with their shopping. Moreover, in order the avoid the "reload" tactic, such events should be completely random, and while X times you buy/collect/steal a possibly enchanted/blessed item it would turn out to be fake, the Y time you buy it it would actually turn out to be real. Also, as mentioned before, one would have to wait for a chance to utilise it in order to verify their "magical" potential, or else emply some esoteric sage.
Thirdly, hunger, thirst and, most of all, fatigue should be introduced. You try to save some coin by buying the cheapest room in the worst inn? Been sleeping two weeks non-stop in the forest? Sure, why not, but now you suffer negative modifiers to reflect just show tired and generally worn out you are.