I haven't explicitly tried to enforce encryption, but probably the drive-by style reports would require extra steps that their automation might not handle. So probably a good first filter. But then I'm still no wiser since the ability to use pgp isn't a qualifier regarding knowledge of the engineer or quality of their report.
It seems that the underlying problem is that those that do good work in this space don't scan the web to find new customers/leads to pitch their service in shambolic ways. And the skiddies who want to make a quick buck will outnumber the good who might accidentally have ended up on your site (because they like your product etc).
the noise/quality ratio in the whole approach is just too big for this to work well in practice. I'm still waiting for the recruitment industry to catch up with the practice and use the security.txt as a sink for people who want to be added to a list of experts that will be contacted when "the company is ready to do a full security assessment post-MVP". I realize this would be fraudulent and I'm not advocating for it - just saying that fake-job offers aren't uncommon either so this will just be a question of time.
What you're describing is a lot like the bug bounty program I ran for a previous employer. It was mostly low-effort scans and "reports" templated from something a big company had made public once. No understanding of if not using HSTS was actually a vulnerability, just the expectation of burp -> report -> $$$.
There were a handful of genuinely good contributors, but probably under 10% of reports.
