their premium members buy at bottom and sell you at the top. Avoid these at all costs. Few other things to avoid are, lending platforms like bitconnect(RIP), davor etc, McAfee - avoid this joker at all cost he is an actual nutcase and I don't think he knows much about crypto projects or have any deep knowledge of any kind on crypto, if you've been following him and his reccommendations you know this already, avoid ICO's with no cap.
Yes. It's true that those people of such groups would have bought the coins which they want to promote at very low price and they would ask us to buy when it's getting pumped. Suddenly when they reach their target of high price, immediately they would dump those coins without our knowledge and we would be left in loss.