If you are using Profit Accumulator or OddsMonkey they will usually have good advice on these and which way to do them. If the rules don't line up you are looking at Dutching (betting on one outcome at one bookmaker and the opposite at another) which is a bit more advanced than standard MB - tools for this you will also find on the two sites I have mentioned. The retirement rules can be found in the T&Cs of the bookies/exchanges, and you need to check how they will pay out if one of the players retires.
A good example of the differences was yesterday. PP had an enhanced offer on Del Potro to win 3-0. A lot of people bet on this (me included). Del Potro's opponent pulled out through injury. PP paid out on the bet, but Smarkets voided the bet. Good for me as I am up on PP but with no liability on Smarkets ;D
Now have a Son in Law, and have become the 'dreaded' Mother in Law. Many congratulations to Hazel and Matt who got married on 10th August, at the Centre for Alternative Technology, Machynlleth, North Wales. It was a fab weekend away and the most unconventional but personal wedding ever!