I think the first signal they share and that is free is to encourage people to come on to their group, but I believe the next is not free anymore you need to work on them or pay for them, but if you sense anything weird in between then it better to leave.
I don't want say more/again about "why you doing it for free".
In any case you have your own right/opinion about it, and if you don't like it or as you say "if you sense anything weird in between then it better to leave".
It's ok
