That was how they used to do things, and I am sure there may be some people who still operate like this.

Modern bookies use juice which amounts to small fees to make profit, balance the books by encouraging betting on both sides, hedge their bets by passing on risk to larger bookies and/or betting sites, and of course ban players if they are winning too much.

The deregulated nature of this form of gambling results in a lot of corruption and predictive betting is even more problematic.