What I experienced is that most of such signal groups might give signals when they personally have experienced a pump or dump. Even most of these groups might be manipulating the price of some small volume coins by creating false pump and than they might swing their members from their groups to place buy orders after the pump is already been performed just to create demand and buy orders for them to sell instantly.

Minor cases happen when the coins pump again giving profits but majority of times, people end up buying lower volume coins at the peak which would hardly be reached again which would indeed leave them with loss only.