Interestingly, we've just received a parcel, delivered using SD, that was overweight. Here's what seems to have happened: 

The weight has been written on the label: 2750g against a 2kg limit. The parcel has been delivered, with a sticker saying £5 charge plus £1.50 handling but we, the recipient, do not seem to have been charged. I wonder whether this fee will be recovered from the buyer? 

What a bloody mess!