In general terms, market manipulation is possible, but what we should focus on is the kind of market where this chances of manipulating market price is very possible and feasible, in cryptocurrency, i don't think it's possible with bitcoin but can be possible with other cryptocurrencies since their market value is determined by the stakeholders who are the major investors on that particular coin, in the open financial and centralized economy of fiat, it is very possible and many are doing it and will always continue with that as long as the decision is being made by some category set of people.