Oh and to add:
To keep people from "cheating," if you try and buy something and then sell it for more than it's original price, it won't sell. Consignment stores don't sell everything, and this is kind of a fun way to do that.
It's not something to make a profit on. It's something just to sell old stuff for more than it's depreciated value and make a little money.
For paintings and books though, it will be kind of a different story.
And to clear up what I was saying:
Let's say you buy something that originally costs $1,000. If you try and sell it for $2,000, it won't sell because it's more than it's original cost for the store. On the other hand, let's say it's depreciated value is $450. If you price it for $600, it will sell because it's less than it's original cost.