Thinking outside the square here? If the pro punters (making a profit Backing) can't get on with all the online bookies, then they must take their turnover to Betfair, Totes or Oncourse bookies.
What proportion of the punting turnover would be represented by the pro's compared with the amateurs? Do the successful punters, 2% of the punting population, provide say 50% of the turnover? If it's a significant proportion, this will help ensure the viability of the alternatives to online bookmakers. Considering the cut throat competition for the mug money, they must be cutting margins to the bone and hopefully a few will go bust?