Its not as safe as buying through Amazon market place, but Amazon can cost more (certainly if your are a seller).
Still I have (generally) had a good experience with even when I have had a problem. I bought COD 4 and the disc was scratched and would not load, wrote to seller and he told me to return it and I got a full refund. Paypal is not the safest though, Amazon is much safer.
I have also bought other games (new and sealed) and then sold them for more after I have played through them!!







