There is money to be made providing vetting services as well as insurance services. You could argue that all parties offering either of those services are 100% going to be fraudulent, but this only makes sense if you assume that there is more money to be made acting badly than by developing a legitimate reputation for being honest.

In a group of actors, trust is a good thing. It benefits everyone, and everyone has an incentive to foster its development.

In meatspace systems we rely on things like identity verification (id cards, green bar certs, fingerprints, retinal scans, etc.), reputation by affiliation (resumes, schools attended, firms worked for) and and testimonials from others we trust.

The key aspect of the above is that we don't have to trust any of those signals perfectly in order for it to be of some benefit. If I find out someone went to Harvard, is followed on Twitter by Marc Andreessen, has had five commits accepted by Linus, has a credit score of 675, uses Android, has bad breath, etc., I will take each of those signals as some indication of her credibility on various issues and formulate my meta-opinion about how/whether to trust her based on some heuristic.

When I order from a seller on Amazon with very few stars I take a similar risk, yet once in a while I do so. Some fraud is taking place on Amazon but on balance the system gets more trustworthy every day.