Small shops can do well, our smallest shop had many Crooks and Crannies and undisclosed corners, the big punters loved it as they could count their cash in private, see both the 'Board' and the sporting life racecard from their hidden area and make their bets without anyone seeing anything. And all the work was "Under the Counter".
....... any regular had what was called an "Under the counter" account, they would present their bet as £2 on whatever, but the meaning of £2 was actually £20 but the Tax was paid on only the £2 but the full £20 would be paid upfront fer the bet and the .40 pence Tax on the seemingly £2 bet would be waived by the Bookie.
The small shop would do well to do even half of the dockets of what a usual shop would do, but when it came to takings, it could easily Double any other regular shop.
Obviousely not a true story.