It seems manipulators exist in any investment markets.
But since Bitcoin is still unregulated (maybe never will) , those guys can do whatever they want to reach their ultimate goal -  making a lot of money.
My strategy is simple: when those guys tanks the spot price, I buy.
I am keep buying month after month.
I do not spend a lot of money to maintain a normal life, I can put the remainder of earnings into Bitcoin when prices moves lower.