I'm not talking about manipulation. Just someone with lots of coin ( that they have acquired at very low prices) that feels like cashing in a few... thousand... and the cost is almost nothing to him.
i think i understand what you're saying -- for fear of talking at cross purposes, let me clarify what i meant:
say he picks a 'bad time' to dump -- the worst time would be at a market bottom. if he does so, there is a 'cost' of lost profits. also, if the market is 'ready to go up', a dump is just going to be picked up by smart sellers, and there would be very little effect at all.
as such, buyers and sellers don't really have a direct effect on the price, but mesh with 'market conditions' to produce the effect on the price. following from this, you don't have to predict the individual actions of large players, just anticipate the possible effects of any action on present market conditions (which are given by some methods of TA).
--arepo