Using a betting exchange for the first time can be confusing, so here is a recent reply to a question asked by a newcomer to matched betting.
Can you explain the back and lay markets on Betfair?
With the betting exchange (in this case Betfair) if the bet has been matched then it is a valid bet, unmatched bets are bets that have not yet been taken and are waiting in the queue. For example:
If you were to lay a bet on the Tottenham you could do so at 4.1 (this is the lowest odds available (in pink), this would then become a matched bet. If however you wanted to offer odds of 4.0 then this amount would queue on the back side (blue side) for someone to take and would remain unmatched until it is done so. Your money would join the end of the queue and be added to the £94 already there, once the money at 4.0 is taken then your bet would become matched.
When looking to match a bet for matched betting purposes it is ideal to find a bet (at the bookmaker) that has as close odd as possible to the lay side (pink side) at Betfair. You would then place the bet at the bookmaker and lay the correct amount at Betfair. For example say Ladbrokes were offering odds of 4.0 for Tottenham to win you would back this amount (say with £10 for example) then using the spreadsheet or the matched betting calculator you would calculate the lay amount in this case it would be £9.88 which is the amount you would place the lay bet of at the current odds available of 4.00 (assuming 5% commission).