Back then, a particular provider was significantly slower (5+ minutes) than the rest and all bookies using it was 'going behind' the odds movements - ups or downs. Soon after many people started exploiting this, the bookies changed their TOS and started cancelling bets.
...which is pathetic imo
They (the provider) should have just fixed the issues on their end, instead of kind of forcing their customers to bully their customer/punters then. But I guess the bookies liked that "tool" in the end 
Another scenario, which would only work in smaller markets/sports though:
You have a flagged and heavily limited account in a bookmaker. Early odds come out, player A vs player B, 1.80 - 2.00. You want to bet on player B, but with higher odds. So with your flagged account you bet on player A multiple times max stake (because of the limit, you can't stake a lot though). Odds move of course, and are maybe 1.60 - 2.40 then. That is when a friend of you with unflagged/unlimited account places max bet on that 2.40.
Into what kind of category would that fall ? Exploit ? Scam ? Market manipulation ?