Yes, this is a tough issue, for people with lots of money, and for poorer people it becomes a great issue, because we cannot spend the true value, yet we still want the item, but for people with the money, they tend to want to make it fair for the seller. BUT, I will say this, I dont think anyone here would turn down a $5 altair sitting on a table at a yard sale.
It depends on the buyer's position I guess, sellers should always do research before selling an item however. Ignorance or laziness cannot become an excuse for people to expect someone to offer more for an item.
Also, in a situation where I was dealing with just one item, not a yard sale or such, I might offer more than asked, but if it were a yard sale or such, I would definitly grab that baby, pay and run.