Taxation on bets
A few bookmakers may charge a tax on your bets, depending on where you reside or where the bookmaker has its license. We’ve developed a solution for this tax where you can specify which taxation method (if any) is applied to any bookmaker account. The sure bet / value percentage will then be adjusted accordingly, fully automatic of course. You can find this setting under Options/Bookmaker.  You can select each bookmaker in the drop-down menu and specify tax settings individually.
There are different ways in how bookmakers handle this. Some take 5% of the profit or 5% of the stake, others chose to completely ignore it (doesn’t charge any tax on your bets).
Two examples:
Bwin
“For all bets lost, bwin will cover the entire taxation amount. Only in the case of won bets we will retain a 5% fee of the winnings (gross) to partially cover the tax burden.” We call this taxation of profit
https://help.bwin.com/en/sports-help/mobile-sports-betting/betting/bet-settlement/taxation-on-sports-betting-in-germany
Bet-at-home
“Stakes on sports bets made by customers with a permanent or habitual residence in the Federal Republic of Germany are subject to a taxation of 5% due to the Race Betting and Lottery Act of 1st July 2012. When placing a bet, 5% of the stake will automatically be deducted. The calculation of the possible winnings will be based on the reduced taxable betting stake.” We call this taxation of stake
https://www.bet-at-home.com/en/terms