No market that was transparently being manipulated, or even suspected to be, would have any buyers. Only sellers. Or, vice-versa. Thus, there would effectively be no market at all. It takes a buyer and a seller coming together to establish a price, each thinking he has the better deal. One thinks it is not going any higher and will soon go lower, the other convinced it is going higher still.
Commodities markets have been manipulated many times throughout our history. Steel was at one time as were other metals. Remember silver and the Hunt brothers? Everyone knew what they were trying to do and there were plenty of buyers, all thinking they would also make money on the runup. That's the case with oil now. All the players, except maybe the retail gas stations, are making huge profits on the runup. There is no incentive to get off the train except the possibility of a crash and we have seen by the stock market crashes how reluctant investors are to believe that prices really do come down. They will, it's only a matter of how fast and how far.