SportsInteraction (SBR rating B-) canceled a player's wager on the Wimbledon doubles match Mahut/Clement vs Fleming/Skupski. The winning wager, which he staked €110 on, was voided after the completion of the match. SportsInteraction's position is that there was a clear odds error. At the time of the player's wager, 5Dimes (SBR rating A+) had odds of 1.64 (or -156) on the match. The player's ticket was for 1.83 (or -120).
However, the odds on the match opened at approximately -120, which is what the player wagered. The day before the doubles match, Nicolas Mahut played a marathon match with John Isner which ended up being decided 70-68 in the 5th set. Oddsmakers felt Nicolas' physical endurance after the record-breaking match would be a questionmark that should effect the price of the doubles match, so the market was updated. SportsInteraction failed to react to this odds change.
This is commonly referred to as a 'stale line'. A stale line is a result of a linesmaker failing to update the odds of a particular event, as opposed to a 'bad line' which is a clear and obvious clerical error, such as a reversed pointspread or moneyline. In this case, SportsInteraction cited a bad line rule and voided the winning wager after the match ended. SportsInteraction has canceled bets after the events began before, as was done in this December 06 sportsbook dispute. As the odds the player accepted were in-line with the market at one point, SBR has suggested that SportsInteraction pay all wagers on the stale line. SBR will update this report pending SportsInteraction's decision.
There are two kinds of line issues. In one case, a bookmaker mis-types a spread. For example, instead of entering +4.5, he puts in -4.5. That type of mistake is clearly a bad line, and is normally voidable (unless made in Las Vegas, where it must be honored).
The second kind of line issue is from being "asleep at the wheel". For example, the opening spread on an NFL game is +4.5. News comes out that half of the team has the flu, and many players are downgraded to questionable or out. The line moves from +4.5 to -4.5 (the healthy team, which was an underdog is now favored). If a book did not move the line as the market shifted, that is not truly a bad line. That is actually a "stale line".
Generally, bad lines are voidable, and stale lines should be honored. If a book could void any bet on a stale line, all steam-bets could be voided.
It appears that in this case, the player bet into a stale line. The line was good when it came out, but the linesman was not paying attention to the market. If this is just a stale line case, I would normally recommend that the bet be honored (and close the account afterward, if you do not want this player).
There is another issue that makes SIA's position more precarious. SIA waited until after the event was completed to void the wager. While this is not practical all the time, a book is given a much wider latitude in voiding if it does it before the event starts. In this case, I still don't think it was a bad line -- clearly a stale one, according to your history.
My recommendation would be to pay the player, and close the account. Did the player know it was a stale line? Clearly yes. But players betting into steam or stale lines generally keep their wager (and frequently have their accounts closed)