I can't call this a scam even if they are not sincere with what they say, so long as they are frequently issuing betting signals to you, they've delivered their own end of the bargain.
It only becomes a scam when there’s money involved. If a betting group is asking you to pay to join in exchange for betting signals, then it’s probably a scam. In gambling, the results are unpredictable, so how can anyone honestly give out tips on which team will win, instead of just betting for themselves if they’re really that good at predicting outcomes? That logic alone should make you question the real purpose of these groups; most likely, they just exist to scam people.