I bought 7 games (1 GBA, 1 GC, 1 Xbox, & 4 PS2) from them when they had the free shipping deal. All cases (box for the GBA game) & manuals were in perfect condition, not even fingerprints! The discs (cartridge for the GBA game) were in near mint condition. I couldn't find any scratches. It was like I bought them new.
The best thing about buying from GameFly is the cases and manuals, they go straight into storage, and come out in near perfect condition. YMMV with the discs, depending on how popular the title is and whether or not they actually rented the disc they sell you. I highly recommend GameFly used games over EB or Gamestop. At least you know they will come complete and the cases won't have 300 unremovable stickers covering them.