It would not be done here, but using independent bookmakers abroad. I would have thought round 3 was the most obvious choice for this fight, I usually pick round 3 in these heavyweight mismatches as it offers slightly better value than rounds 1 and 2.
The Bookmakers also reported unusual Betting patterns and this was most likely the reporting source of the complaint. In the case of Allen and Darch, the inner circle of friends are likely to be the big beneficiaries.
No way would an independent bookmaker abroad price up the round betting in a fight between Dave Allen and Dorian Darch.