I disagree with you on that 'they have every right to do so'
If a bet is in a status where it can be rejected by the oddsmaker, then it is only fair that the person placing the bet has the option to cancel it as well, especially over a long period of time.
That is not the case with sportsbet.io. Once I hit submit, I am at their mercy for the next few minutes and have no option to cancel, while they can hold and hold and hold and hold and decide what to do.
I think its their way to reject a bet. Not a good way agreed, but its not as good as sites like directbet which show you the max bet and usually don't reject bets. They can certainly be doing what you say they are.
Regarding this topic, please note that we do not manually process large bets, all bets are confirmed automatically by our system regardless of the height of the stake.
In case of a Livebet it can take a couple seconds more as the odds are changing in real-time and in some cases the bet can be rejected as a result of that.
To have the highest chance to have your Livebets accepted you can put a checkmark in the 'Accept all odds changes' box, this does mean you accept any odds change.