Those people are a special bread of people. Being a beta tester requires a way of thinking that is often not the norm. It also takes a person that is keen on detail and has clarity of thought so that he can put to paper his actions that lead to an erroneous action or response from the platform.
Now take that to the game beta tester. There are some that want to go in closed beta in order to play the game for free. They will not take notes on their actions as to identify bugs, they will not try many combinations of the same action but only the one they conceive as being the most efficient way to complete their goal (which is to level up, not to test the game), they will not report things they consider a simple annoyance but will just power through and ignore it.
Those people hurt the games we love but the industry seems to not do anything about it. I consider myself an above average beta tester and have been included in many a beta. Were such thing as a Beta CV I would have a very nice one, but such a thing does not exist. Companies that post applications for closed betas mostly do not ask anything about previous beta experience, and no company has ever provided me with any feedback or certificate or reference for beta work I have done.
Maybe it is time for a change? Or does the current system actually work with the in house QA team being sufficiently effective that the need for qualified beta testers is diminished and thus closed beta invitations are serving another function?
Perhaps there is a third option, that unpaid beta testers are actually so conscientious that there is no need to actually have an interview like platform.