Thank you for catching this. Now I have added a negative tag to both profiles, which I think should deter most account farms from cheating in the future (you can't get into most bounties if you have a negative feedback from DT1).
Nice to see that, case closed.

I might also start requiring a certain amount of activity in order to participate, but I haven't decided by how much yet.
Only activity? I would say it's better to have certain amount of merit too. Probably 30-50 merits because someone can earn 10 merits easily by begging i.e. earn 1 merit and then post an application on rank up thread.
My personal suggestion, I guess someone who earn 1K merits can participate too because there's no shame for high ranked user to learn technical thing from the basic.