Is it safe to buy second-hand games for my PS3?

of course it is .it will cause you no problems if you use 2nd hand cd's

Yes. I am working on a platform that enables users to buy/sell used console games and I can safely say that purchasing used console games are safe and they work out cheap as well. Once done playing, you can resell them and recover most of your costs. Try  https://play.google.com/store/apps/details?id=com.manye.hanchu&hl=en (beta version). I have put up my PS3 games and our game upload policy ensures quality is retained. Hanchu is a peer-to-peer platform for buy/sell used console games. It allows sellers to set price of their game, and if somebody purchases the game, platform provides door-to-door logistics services including packaging. We want to build a community of gamers where they can resell their games at a click-of-a-button to other gamers at a fair price (market price of used console games) and in return, the platform enables door-to-door service like payment, refunds, pick up & drop off facilities. Users can buy a game, play it and resell it on the platform to recover a fair bit of money spent on their games. The app is available in all Tier-1 cities in India. Disclaimer: Co-founder of https://play.google.com/store/apps/details?id=com.manye.hanchu&hl=en, a peer-to-peer platform to buy/sell used console games.