According to Wikipedia, "buyers remorse" is the sense of regret after having made a purchase. It is frequently associated with the purchase of an expensive item such as a car or house. It may stem from fear of making the wrong choice, guilt over extravagance, or a suspicion of having been overly influenced by the seller.
This is all true, however, when it comes to shopping at thrift stores, yard sales and estate sales, buyers remorse is usually defined differently. It is usually regret for having NOT purchased a certain item. In a market where everything is truly one of a kind, there is more often than not, no turning back to buy said item if you change your mind about it. It's not like the thrift store racks are stocked with multiples of a certain dress or shoe. If you do go back to buy something you passed up, you will be lucky if it is still there.
Maybe we should call it thrifter's remorse. I don't know. All I do know, is that I'm feeling it bad right now. Recently, I passed up a large stack of about a dozen road maps from all over the U.S., an owl painting, a tweed suitcase and two pairs of gold shoes. What was I thinking?