It could also be one of the gen 4s with the brass-in-the-face feature and he is willing to get rid of it at any cost. If it's a year or two old he may have only paid $499 for it and is selling it for about the going price for a used gun.Here is an example of listing I would be cautious about since the price is reasonable considering these days. It could be nothing more than a guy selling it for a reasonable price in an unreasonable time but you have to do your homework.
ARMSLIST - For Sale: Glock 19 gen 4