This. But OP wanted special requirements to open a PR. I.e. if those requirements are not met the PR is never visible to all and so admins can reject spam PRs without giving them a platform.
This is time consuming.
Unfortunately the PR and the PR author will forever be listed there and linking to their product anyway.
If they've been doing that to the other repo (and especially if they're just a spam account), there's a good chance using the "report" button and/or contacting GH support directly can yield positive results, up to the spam account being deleted (and the PR is usually deleted).
Unfortunately this doesn't scale.
Correct. I used to report them, but 3/4 years ago they made it more difficult to report anything because you have to explain what's wrong even when it's very clear.