Bitcoin market & community is powered by its users only.

Thus, no one can directly affect or change the market price.

And no one can force a change of its protocol, Bitcoin can only work correctly with a complete consensus among all users.

Although the market of Bitcoin isn’t so deep like national currencies (EUR, USD etc…), thus a large amount of sell or buy could comparatively easily affect the market price.

Also, while trading with a Market Maker broker or exchange, it is possible that the offered prices are modified without prior notice.