Alot depends I think on what type of things you sell. We mostly sell shoes and one listing can have up to 8 colours and then up to 12 sizes in each colour. So there can be 96 variations on just one item. So this I think greatly increases the chance of error. Also shoe factories are often supply incorrect sizes or for instance 2 left feet instead of a pair. 

Perhaps as suggested by others that I am better to send these out regardless and avoid a defect. Rather than be honest and avoid wasting the buyers time........