The guy clearly has the same betting pattern from his old bets compared to the current bet which fixed match is being accused based on the betting history you provided with this screenshot.

The bets was placed on different date with huge gap. Judging from the betting history, he is just having a tough luck or probably following a good bet call. I believe the higher winning percentage is what fuel the fixed match accusation but the guy is using your platform for many months with same betting pattern.

He has a solid insider info if all his bets is from a fixed match. You should just restrict him rather than banning him if he is winning frequently.