I've had a bit of a look at this seller's catalogue and doubt if he's buying wholesale at all now. All of his titles seem to be older, couldn't see anything that jumped out as being a new release.
I suspect he is buying old stock from some source/s at rock bottom prices. Now that could be buying anywhere from a distributor themselves, right through to your average corner games shop that is liquidating old stock.
Maybe an idea there for you, stick your head in some doors and see what is available by way of old stock taking up valuable space on retail shelves. Remember, in the real world a store owner can't afford to keep slow moving stock on the shelf, that's valuable space that can be used to sell fast moving stock.
That of course isn't a factor in online retail as most of the stock is sitting in boxes in the spare room : )