How exchange bets get matched

On a betting exchange, your bet only counts once it's matched. Here's how matching works, and how liquidity and the in-play delay affect you.
You don't bet against a bookmaker. Every back bet needs a lay from another customer at the same price. If nobody wants your price yet, your bet waits in the market as unmatched.
Say the best back price is two point nine, but you ask for fifty pounds at three. Your bet joins the queue. Then another customer lays thirty pounds at three. So you're thirty matched and twenty unmatched. If the team wins, you're paid on the thirty only, sixty pounds profit before commission. You can cancel the other twenty until it's matched.
When the match goes in-play, exchanges usually cancel unmatched bets unless you chose to keep them. Check the setting, because a forgotten bet kept in-play can get matched after a goal.
Liquidity is the money waiting at each price. Say you back five hundred pounds at two, but only two hundred waits there. You also take one point nine nine and one point nine eight, for an average of one point nine nine two.
In-play, bets wait a few seconds before they reach the market. Your price may still be there, or it may have moved, or the market may suspend and cancel your bet. So look for money several times your stake, trade when the game is quiet, remember TV pictures lag behind, and check your open bets before you leave. Please bet responsibly.