Due to lots of scams and frauds then its never been recommendable for you to join up those paid groups.Unless if they were free then you could really join up if you wanted to.
Even for free, most of those groups has something for you to take even they don't charge you. And that's your participation to the ads that they might send to their members.
If you think that you're okay with that and that's the benefit that they can only get you in return of earning some good rewards from their signals, it's up to you if you're totally okay with that exchange.
but what i know is actually not ads taken from that group member but when he gives free signals for trading and a while later he will definitely require group members to pay premium trading signals.
so the free signal is part of the group's promotion to attract a large number of members after the number of members is already a lot he will give a monthly rate as a trading signal.
and for the problem of paying for trading signals it is said to be fraudulent or not it depends on our analysis to the owner of the group. if the owner of the group has a large, well-known community and has many channels such as you tube etc., most likely it is not a scam.