Amazing Discoveries at Booksale

I'm always looking forward to my weekly visits at Booksale. There's always something I'd find and I'd wonder how they manage to get these books (and sell it at a low price). I'm talking about some RPG books that have recently invaded the shelves of Booksale. They are usually priced around 325 pesos, which is cheaper than what is being sold at hobby shops.

Aside from these 4th edition D&D books, I also came across some Eberron manuals for third edition and a d20 Modern supplement book.