Generally it is a nice idea, however it could be tricky, because of the security experts side.
Like you said, experienced people would not use it, because they make enough $$ in in the industry.

So you will mostly get people that are new to the field. The problem is now, that you do a "security check" but people that are not that experienced may miss vulnerabilities. So in the end you maybe pay someone to fix something and thing your site is secure but it's not.

Would be also a legal question if the security researcher may be accountable.