When you receive an order for an item that costs a lot for shipping and needs some kind of equipment, this is an ideal opportunity to make a ‘friendly’ extra sale. For example, if someone has just bought a computer, you could send an email like this:
“I’m just emailing you to ask if you’d like a mouse or a keyboard – since you’re buying a computer from me, I can throw in any accessories you want without charging any extra shipping. If you’re not interested though, then don’t worry about it – it was just a thought.”
Note how informal this email has to be. It can’t stink of sales, or the whole ‘communication’ thing will be ruined. Would you rather buy something extra from someone who says “you might as well, since you’re paying shipping anyway” or from someone who says something like “our valued customers will also love our GREAT DEALS on mice – check it out!” I know what my answer is.