Won a Beta Test Key. Should I mark it as accept as it can Expire after I do it?

Create a support ticket.

Hello, would myself mark as recived, the developer are giving a lot beta keys for the full game now that never expire. ( Have a lot of them) If the key expire someday you can still mark as not recived or contact the giveaway creater.

Many developers using "beta" keys for bundles, because they get many keys before release but after release the additional keys they can get based on the sale result of their games and so many times they can deliver enough keys for the bundles only with those keys. If a developer want to go rogue they can deactivate any kind of keys anyway.

Many times players buying bundles legit can't see it that key has that activation tag, so if it will be common that players show hate to those keys then the amount of given keys will decrease on this site even more. Even worse, on some of those bundles some key might be that activation, some not, so cant tell it beforehand.

Those still activate the full game, I would say best solution is to activate and if it will be ever revoken (which not going to happen, as same activation keys sent usually to influencers and imagine the blame they would do if they lose a key) then via support change the game not received, but if that happen then usually many other will be affected too so it will be a fast service.

For Beta Testing doesn't mean the key is beta, it's simply a trick, that allows a dev/publisher to create keys for their games without any limits.
It should be a permanent copy, at least for more than 95% cases it is.

Btw, misuse of giveaway feedback could be also punished, so be careful