@AceOfNinjas You buy an account, if it is secondary or primary
primary : you can play on your regular account as usual
secondary : you can only play on the given account
you log in on the account, download the game, if it is primary you can set it as primary PS4 and play as usual from your regular account, but if secondary only from the given account, yes the account can get banned if the creator uses a stolen credit card / charges back with the bank etc, or the games get locked if the original owner recovers it and deactivates the games from the site. it is not safe but you can take risks by buying from very trusted members.