Where I work, we tend to do our stake factoring by limiting the punters who basically find arbs.
Even if they win thousands, if they do so by big bets at poor value, we actually ramp the stake factor up and allow them to make bigger bets to get our money back.
My tip would be;
Bookies derive the over/under goal quote from the supremacy quote between the teams. So, if there is a clear favourite, the over price will be low and if the odds are even, they'll be high and you can find good value from this.