Arbitrage betting (or "surebet") means backing every possible outcome of an event, spreading stakes across books with divergent odds so the return is positive regardless of the result.
It is not fraud: it exploits pricing inefficiency between operators. Even so, almost every terms of service lets the operator limit or close accounts that systematically operate this way, because an arbitrage player has negative expected value for the book and no retention value.
Signals that typically identify the profile: non-round stakes very close to the maximum limit, concentration in low-margin markets, action immediately after odds movement, no casino play, and withdrawal right after settlement.
The most common operational response is stake limitation rather than blocking, applied per market rather than to the whole account. The risk of an aggressive approach is false positives: an informed, disciplined bettor looks like an arbitrageur on several signals.