A clean sheet bet wins if the chosen team concedes no goals across the match. It is the defensive mirror of BTTS: 'Team A clean sheet — yes' is close to 'both teams to score — no' weighted to one side.
The honest way to price it is from scoring rates: if the opponent averages 1.2 goals per game against similar defences, a Poisson model puts the zero-goals chance around 30%, making fair odds about 3.30. Any shorter price needs a reason — missing strikers, a parked bus — that the averages have not caught yet.
Opponent's expected goals against this defence: 1.2. P(0 goals) = e^−1.2 ≈ 30.1%, fair odds ≈ 3.32. A book offering 2.80 is charging you ~16% over fair; 3.60 is paying you to take the variance.