No, the market is not always determined by supply and demand. Look what happened to gold and silver over the past year. The price dropped, demand went sky high, and the priced dropped more.
It is very much possible to manipulate markets...
The same people that sell something, can be the same people that buy it at the same time.
They would take a loss... but they wouldn't care. What's more or less fiat currency to a central banker?
You cannot compare a commodity like 'gold' that has an 'unregulated supply' to Bitcoin that 'has a regulated supply'. What I said is correct, you are trying to compare things that cannot be compared. (Again, people without qualifications becoming self proclaimed experts overnight)