How important are returns to you? To many here is a disaster and can get very expensive.
Usually we enforce out restocking fees and shipping which is costly for the customer. If it is plain as day that they ordered what they thought they did it takes a lot of the ill will out of the return equation.
However, I will admit we will probably never get these customers back in the future. But they will be less likely to complain publically if it is not a fair complaint.