I heard of the concept of wash trading before, but in the context of money laundering... didn't know you could manipulate prices with it as well. I guess that such activity wouldn't be too hard to spot though as all the exchanges print the time and sales data. So if somebody does a wash trade, you'd see two trades of identical volume but in different directions. I guess that would be one thing to look out for before you buy!
Potentially. They could also use randomly generated order sizes to absorb various chunks of the book through a variety of accounts then let it go bid (or ask) and start again. There are a lot of different ways to disguise activity and anyone who wants to jump in has to be aware of how markets (and those creating markets) operate and manage risk appropriately.