I certainly don't spend 24/7 at a computer, I am rarely there at the time an auction item ends but I make very sure that I quote the correct postage in the first place. If I did't then it is my mistake and if I owed the buyer a refund I would just accept the few cents extra in fvf as a just punishment for being a numpty in the first place.

When it comes to combined discounts I tell buyers to wait for a combined invoice before payng, if they don't and pay individually then they get what they paid for, X numbers of parcels with full postage on each.