Some good comments I've read online:

I recently tried to back a horse for a mate putting $1500 on at $4 and got knocked back and told to ring a certain number. With a minute to go, that wasn't going to happen.
The end is nigh. The industry must compel fixed odds operators to bet EVERYONE to lose a certain amount. If the business model is unsustainable, FANTASTIC. You have no business offering fixed odds if you don't have confidence in your market. Perhaps if fixed odds were only available in a few places, the holds would go up and the book would be easier to balance.
I'd like to see fixed odds only available online if the bookie is on track.

Knocking back winning punters is tantamount to encouraging problem gambling, they tried to go down this path years ago and there was a big stink kicked up about it and they backed away from it in the most part.
I think it could be challenged effectively on that basis alone as the WA TAB is government owned, wouldn't look good for the government to be proven to be actively encouraging problem gambling and if you're deliberately screening out winning punters that is effectively waht you're doing.

Source: http://www.perthturftalk.com.au/dis...to-disappear/p1