I have been betting for years,i mostly trade Greyhounds on Betfair...but also Football and Horse Racing...its the only sports i think i gain a edge.
I also have accounts with about 10 bookmakers,as this helps with getting a decent arb on betfair but you have to work fast.
I also know unless the Managers markets is on Betfair,bookies would limit you to peanuts.
The bookies are not stupid they will no people will have 'inside information' that's why you will only be allowed to have small stake on your fancy.
Jas i think you are telling a big porky pie.