Some clients told the BBC they had their betting accounts closed or their bets "restricted" following wins.
Bookmakers say they limit bets from a minority of customers, to ensure good odds are available to all.
Neil Smith, a techer from Yorkshire, told the BBC he had had around 450 online accounts closed.
He said: "They will just say: ' Sorry our traders have deemed your betting pattern to be unprofitable and we're a business'.
"They shouldn't be advertising a product that's not available to everybody."
Campaigners have called for gambling authorities in the UK to force bookmakers to accept all bets up to a limit and make it clear to all players that restrictions may be imposed.
One anonymous shop manager told the BBC their company encouraged staff to screen-out successful gamblers: "They grade. If they are a serious backer of horses and clearly know what they are doing with the odds then we don't want them at all - the orders are 'get rid of him or let him have a few quid on the starting price only'."
Bookmakers insist they are just trying to be fair to the ordinary punter by restricting a small number of what they call "professional" gamblers.
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