SV does reject con artists, it's just that con artists love to fake associate themselves with SV and then people who don't know any better believe that the con artists are real because of that fake association.

(If you define 'SV' to mean only the major companies, VC firms, and big decision makers actually HQed in SV.)

This isn't a solvable problem, while still remaining a somewhat free country, since roughly half the population will always be below average in sniffing out dupes. So some fraction of con artists will always be able to succeed in duping some folks.

Of course there are a lot of SV entry level and middle management types that go bad since even a 2% corruption rate means thousands of people per annum at SV scale.