Bitcoins price is based on supply and demand on the market.More demand higher price more supply down price.Yes you can manipulate bitcoins price if you hold a huge supply or supply that may be enough to sell or buy in the current market status
Completely agree, I'm sure that happens with bitcoin is natural because of demand and supply factors, and not due to the influence of the pump. It's hard to do the pump because the stock and demand bitcoin spread evenly (no one's monopoly).