The identical scenario also produces disastrous purchases. Beware of people you have never met before offering you bargains. Beware of any situation in which your idea of the value of the object is far greater than the seller's. You may know something he does not. On the other hand, he's lived with it and is liable to know something you don't.
Bargains sometimes come as the result of blind luck but much more often as the result of knowledge.
The best bargain getters are connoisseurs who can recognize quality without regard to names, fashions or price histories. For anyone less well equipped, the best bargain, more often than not, is the right work of art at the right price. The difficulty is that one generation's famous prints are not necessarily another generation's famous prints. The test is to be able to distinguish importance from fashion, not always as easy to do as it sounds. Nevertheless, stolen items do find their way onto the market, sometimes through the hands of respectable dealers who have no way of knowing the item was stolen.