As a toy collector I regularly spend 10,000 baht up a month on FB (bought something 5k yesterday), but I only buy from people that I have many of the same friends with. Have I been caught out , yeah , maybe 600 baht in 8 years on a punt, but I can live with that. since it makes up such a small amount of what I have spent.
Only a complete idiot spends big money with people that they do not know without mutual friends or invest in whimsical investment schemes.
Thieves are the issue, not the platform. You do not shut down an entire open market as someone fleeced you for some expensive dodgy flip-flops !