[Loocid]

Not as much as traditional bookmakers but they absolutely care. Betfair has a "premium charge" where if you earn over a certain amount in a year, you get charged a fee equal to a % of your gross profit.

Its the same as poker. An exchange wants a bunch of equally skilled players betting against each other. If everyone has zero edge, all the money stays on the exchange betting over and over and the money eventually all goes to the exchange in commissions.

Players with a strong edge dramatically reduce the time before the losing players run out of money, meaning less commissions for the exchange.

[piltdownman]

If you earn over a certain amount in a year, and are categorised as a deriving your majority income from gambling in a 0% tax Territory (Austria, Australia, Belgium, Bulgaria, Canada, Czech Republic, Denmark, Finland, UK/Ireland etc...), you can offset the % charged as an expense.

FWIW, an exchange doesn't necessarily want a bunch of equally skilled players betting each other, they want a lopsided book on the bigger markets to attract domestic bookies and match-makers laying or staking across multiple platforms to leverage Matched betting discrepancies on promotions for new players etc...

//Players with a strong edge dramatically reduce the time before the losing players run out of money, meaning less commissions for the exchange.

Poker Players with a strong edge have a +ev Variance. Over 100 hands they're not guaranteed to be a winner. Over 10,000 hands they are.

YMMV massively in other sports, but for horse racing the big gamblers tend to only put down big money once or twice a year on maidens and trial-runners for Cheltenham or Grand National. They wouldn't touch a big festival other than for fun.