l2store sales apply only to trust among members. if people stop buying from him and rest of his kind, it would be clean. (as much as it can be). a good idea would be to make a thread, scammers list, where people post scammers' names with proof of scam to warn rest.
when you are trying to trade with someone you are taking some risks . dont forget that you are giving your money with your will to someone you dont know at all . no one is forcing you to do that . and as etherial says here if you want to avoid such things with scammers you should make a post at forums so you will write (with proofs always) who is trustable and who is not . you have the power to prevent scamming . for example i was scammed a long time ago at freya patch when i gave a dle sword (it was expensive back in time ) from a clan mate !!!! and when i petition at ncwest they told me that they cant do anything since i gave it with my will .