Has anyone ever had to dispute a bet on here?

They could. But you'll never get them to admit it.

I've queried the settling of a handful of markets over the last few years.  Sometimes they resettle, sometimes they don't.  It wouldn't surprise me if ambiguous markets or results were sometimes settled according to which customers would end up winning or losing. 
I've not always been convinced that "fair" comes into it but when you lose a bet, it's never "fair"

Spill the beans. I like a good mystery...

take a screen shot thats what to do now, last week £50 lay on in running price about 2-00 the bet hung not coming back as accepted went down to about 1.4 and them wiped, it won, message came back no bets on this market after the race was over, the price had been wiped on the winner so took a screen shot refreshed a few mins later guess what the bet had been matched at 2-00. been caught many times before so get used to taking screen shots when things hang and it aint your fault.

Years ago I laid something for four hundred quid over the phone. The guy had thought I had said for a hundred quid instead of four hundred quid. After a few phonecalls betfair replayed the tape and agreed I had said four hundred and it wasnt that clear when the guy read it back to me. Said they would meet me halfway and give me £200, I said halfway was another £50, i.e the difference between 400 and 100 being 300 but they wouldnt budge. At least I got something back!

On the 8th December I got hoovered. I put bets up backing the draw, a penalty was given, and my bets were matched before the suspend.

Betfair refunded it, so fair play.

A

A couple of years back had £1k on federer to win a match, clicked on a link on the home page - match betting, took me to the most aces market, from memory the prices for Fed were similar in both markets, around 4/6 and I struck the bet on most aces rather than to win the match. Watch the match,Fed wins, check account and no winnings, Fed lost the most aces market. Queried it with Betfair and fair play four days later they refunded the stake having found the link was incorrect and misleading