You typically sell through a broker to a market maker who are offering a spread to cover their costs and make a mark up. Usually the offer (bid) price is lower than they’ve already agreed to a buyer (ask).Can anyone explain, when you buy shares at say £1 each, and they go up to £1.20 each, and you want to sell them, is there always someone willing to buy them off you? If there isn't anyone willing to buy them, can you not cash them in ?