Being an individual, it is almost impossible to manipulate bitcoin price unless you have few millions to trade in crypto currency market. However, if you have a group of traders with you with good numbers of investment, you may try to put some fake trading requests with good volume and you wish may be fulfilled. But the chance is rare.
Check the market cap of bitcoin. So it is not possible for an individual to fake bitcoin price. A million dollar may come handy there. Just a suggestion!
And that is the most important reason why it is very difficult for the manipulation of bitcoin price even going beyond individuals to more than 200 people. Bitcoin is so dispersed to make all of us agree an impossibility starting from the differences in time zone to the changes in offer price in our individual countries, volume is another thing among other factors that will mitigate against our agreement...
May be if you have tons of bitcoin from the past, you can really manipulate it well and it will be easy to control the market. And only groups of people that can manipulate it unless there is a person that hold bitcoin long enough to wait for this moment and control everything on market