The one thing I have confidence in is the voting. After the BBC voting scandals in 2007, everything changed and was tightened up. The other big deal about the voting though, is the short amount of time we have. Since they started recording the Sunday show straight after the Saturday show, it means there's hardly any time to vote. An auditor has to sign off the voting, so the time constraints are tight.
But there's plenty of other ways to put a couple at a disadvantage. Choice of dance and music can be big killers, especially now the couples are told what they're doing by the producers. For at least the first 5 or 6 series it was the pros choosing the music and in the first 3 or 4 weeks couples would dance one of two dances each week, and alternate Ballroom and Latin. This meant a more level playing field, as opposed to now where couples can be dancing harder dances early on in the series.