What they are talking about is what constitutes a valid match if one of the players pulls out part way through due to injury. Some bookmakers need the whole match to be completed otherwise the bet is void (such as Bet365), others (and this applies to all the exchanges) only need one set to be completed for the bet to stand. So if you bet on player x @ Bet365 and lay @ Smarkets and he pulls out injured in set 2, your bet is voided @ Bet365 (money returned), but the lay bet @ Smarkets is still valid so you lose that.Can I ask what does it mean then when it says the rules don’t match ?
As Bet365 has 2UP this is the one used a lot, but you are taking a big risk if you lay it at the exchange. Therefore people are advised to use Dutching where you place a back bet on player x @ Bet365 and a back bet on player y at another bookmaker that also has the same rules (a draw is not a possible outcome as one player always goes through).
Oddsmonkey has a list of all the different rules, and also a tool to find Dutch matches - not sure what PA has these days.