I don't agree with you when you say its fair for "both" side when they count after player retires in second set because most of the time Big bettors will bet on over or under games . Under wont be a problem , but " over " ?
Haha
forgot to mentioned that, under/over bet will be all void in Direcbet if the game have been cancel. Take a look to this all this rules if you're still confuse to the Directbet sportsbook tennis rules.
•If a player or pairing retires or is disqualified in any match, the player or pairing progressing to the next round (or winning the tournament in the case of a final) will be deemed the winner. However if less than one set has been completed at the time of the retirement or disqualification then all bets relating to that individual match will be void.
•All bets relating to the number of occurrences of certain events within a tournament will be void if the tournament is reduced in length, postponed or cancelled, except for those which have been unconditionally determined.
•All bets will stand regardless of changes to scheduled venues, including any changes to a different type of surface.
•If the scheduled duration of a match is reduced or increased in the number of games/sets required to win, all bets will be void except for those which have been unconditionally determined. Please note that this does not apply to ‘Match Odds’ or ‘Set Winner’ bets on Davis Cup matches or ‘dead rubber’ matches that have been shortened from five sets to three sets after the bet has been confirmed, provided that the match has been shortened in accordance with the competition’s rules.
•Where bets are offered on individual games or sets within a match, a retirement or disqualification during a game or set will render bets on that game or set, and all individual game or set, void, except those which have been unconditionally determined.
•If a player retires before the completion of the match all game handicap bets will be void, except those which have been unconditionally determined.
The special 'Player Progress' bet is on which stage of the tournament will the stated player be eliminated.
•Any player substitution during the match WILL NOT have any impact on the way the bets are settled.
Of course, different sportsbook have their own different rules. All the rules I post above is from the
https://www.directbet.eu/Rules.cshtml