TERM
Negative surebet
Bets on every outcome at different bookmakers where the sum of inverse odds is slightly above one: a small guaranteed loss instead of a profit.
A negative (minus) surebet is a set of bets covering every outcome where 1/k₁ + 1/k₂ is slightly above one: for example, 1.95 and 1.95 give 0.513 + 0.513 = 1.026, a loss of 2.6% of the bankroll whatever the result. By definition there is no profit here; the point is that you know the result in advance.
It's used to clear bonuses: a bookmaker grants a bonus on condition that you wager the amount several times, and each bet on one outcome there is covered by an opposite bet at another book. The player loses a few percent on the odds difference but gets the full bonus. Some scanners sell such pairs as a standalone product; Dozor only looks for positive surebets.
The risks are the same as with a regular surebet, plus the bonus rules: minimum odds, a ban on “hedging” at another book, market restrictions. Breaking the terms voids the bonus, and the loss on the bets stays with nothing to offset it. Bookmakers cut limits for this kind of play faster than for ordinary single bets.