Further to this post,
A practical example from yesterday shows the problems we punters encounter in our efforts to win in the long-term.
I invested in a trotting race at Wyong with the required number of runners to pay three place divs. However, mayhem ensued and a number of horses fell and dislodged their drivers. It was declared a no-race and rescheduled for later in the day. However, with scratchings, there were to be only six starters in the rescheduled race, meaning only two place divs. Upon hearing of this I contacted the TAB wishing to cancel my bet as the circumstances had changed dramatically and the odds, in my opinion, were now stacked against me. I was told that as I had invested on the internet that I could not cancel my bet and despite my protestations the bet stood.
Well, justice was done and my horse won in the six horse field and paid well for the place.
Yes, I won, but my point is that in all likelihood I would not have bet for the place in such a reduced field. I should have been given the option to cancel my bet as circumstances had changed so dramatically.
It worked out OK this time but overall I think it works against the punter in such circumstances.

Cheers.