Experience can be assessed by asking for LinkedIn/website/resume and checking that. This will probably suffice for the 90%.

It's not going to be foolproof. Just because someone has good experience in their background doesn't mean they're good. But neither are interviews foolproof. They can be gamed.

I wouldn't need to prove to companies that the vetting is valid. They can see the results themselves. The platform would die if the bar isn't maintained.

LinkedIn _is_ a free for all. This would also be anon by default and double opt-in for devs.