Adonai, I think you are more concerned about the quality of second hand PS4 games rather than their region compatibility, am I correct?
If so, it's always YMMV. Some brokers of second hand games do not bother to check the discs for scratches and what-have-yous. If you happen to buy a damaged disc, then the game won't work. So try to buy from reputable sellers, and if possible, check the discs yourself before paying for them. Also, if you're buying here, make sure that the return/exchange policy is clear before completing the transaction. Due diligence, as they say.
Now, what I can tell you is that, compared to older generations, PS4 discs should have less wear and tear if handled with an average amount of care. This is because every retail PS4 game is installed on the system's hard drive, and once installed, the system will only read the disc when booting up a game, similar to how most retail PC games from the last two decades operated. This is unlike previous gens when the systems will always read the discs to load up data.
The cons of buying second hand PS4 games?
Well, it won't smell new. I know, I know, this is such a shallow issue, but many gamers actually love the smell of new games, much like how many bookworms love the smell of new books.
Also, some used games won't have their corresponding DLC codes, if they were released with the retails discs. Worse, most DLC codes, once used, cannot be used again for another PSN account. You will have to buy these DLCs from the PS Store. You're planning to purchase Infamous: Second Son, for example. Infamous has a Day 1 DLC (supposed to be a pre-order bonus but it wasn't that exclusive upon release) called Cole's Legacy. If the code has been used by the previous owner, you won't be able to play this 1 to 2 hour adventure. Same with Assassin's Creed IV with its, what, 9 or 10 Day 1 DLCs?
Luckily for you, Sony has disallowed the usage of online passes, something that FIFA 14 and Assassin's Creed IV planned to implement. You can still enjoy online modes for your used games, for as long as you subscribe to PS Plus.
I hope this helped!