The Pumper needs liquidity to exit his positions, and gets people to buy the stock so he can exit his large position slowly. You can simply avoid this buy not doing anything! If you do nothing, then he is a current large holder of a coin! Which means he may not ever be able to exit his position.
So if you think you know someone who is possible tricking you into buying a certain COIN. Its best to get all the people he's tricking together and not buy his next magical high % gain pick. By avoiding buying at all this fellow can be stuck in his low coin. GOOD LUCK!