..... can i ask what was the biggest amount of lolly you saw someone win and lose.
I didn't answer much on biggest losers fer me as a bookie, but I have a few thoughts ....
I can't really think of any one big winner apart from 'Crystal Ball', but there were a good few real Bad days in the bookies.
Dawn Run and Johnjo winning the 1986 Cheltenham Gold cup, on my first week as a senior settler in the main office.

The weekend in 1982 when
ALL the hot-pot favs won on the football coupons.

Tirol the Cork owned horse winning the 1990 2000 Guineas at Newmarket.

Tirol the Cork owned horse winning the 1990 Irish 2000 Guineas at the Curragh.

Imperial call the Cork horse winning the 1996 Cheltenham Gold cup.

Frankie Dettori doing the Magnificent 7 in 1996.
Mind you we did dodge a huge bullet that day as a regular customer of ours went to Ladbrokes that day to place his usual morning large multiple bets which always included Frankie's mounts, his winnings came to £120,000 and to be fair to Ladbokes they waived their £100,000 payout limit that day.
There were also many big winners on the Lotto when we started betting on it in the late Eighties, those winners were a bug-bear of most bookies because unlike Horse or Football betting winners whom would usually lose their winnings back within a few weeks, Lotto winners bought new TV's or house furniture and continued betting with the same stakes.