It might seem that is correct until you bring volume into the...

It might seem that is correct until you bring volume into the equation. If you buy much less than you sell to raise the price and other buyers are prepared to buy at the price which has been raised then you can sell more than you bought and come out in front. This usually only works with quite liquid stocks where there is good turnover daily. Some call it market making others name it in more derogatory terms. You will often pick it happening when very small amounts of shares change hands with some frequency on either side of the market.