Overround explained

Sum the implied probabilities of every outcome in a market and the excess over 100% is the overround: a 1X2 summing to 105.5% carries a 5.5% overround. It is the same object as the bookmaker's margin, just measured on the whole market rather than described as a fee.

Overround varies by market and book — mainstream leagues at sharp books run 2–5%, exotic markets and small leagues 8–15%. Checking it takes thirty seconds and tells you what the table stakes are before any opinion enters.