Not necessarily, if no one is willing to but at current price then they will set a limit order at a lower price waiting for someone to sell at lower a lower price.

It's much more complicated than that because you also have market makers. I think there's a website caled www.investopedia.Com that can answer just about any question you have.

If you don't find your answer there then pyruvate message me and when I get a bit more time to elaborate a detailed answer I will do that for you.