I'm not in any Facebook groups that do comic raffles, but there is another collectible group (for concert prints) that I'm a part of that do them. They always base the winning number off of the Powerball or Mega Millions drawings, so there's no way for them to be rigged via random number manipulation. It's actually not a bad system for that type of sale. I think I've only participated in them twice, and I won once (an extremely rare print, and I only personally paid 10% of the value).
I have done a comic raffle on Instagram, and won my first one. I'm not typically that lucky, so I think that's the last one I'll do. 😊