Yes, and that's exactly how the middle man is compensated for the risk they take by buying something from someone they don't want, hoping to resell it shortly after.
If this happens on an exchange (such as Coinbase), there is no risk, since the trader/middle man knows that there is a buyer for 140 and a seller for 120, so he can 'front run', buy at 120, sell at 140, keep 20.
