I have had a problem with a buyer combining purchases which meant the Simple Delivery system did not cover postage due to the weight of the goods, I had to pay over £10.00 extra to post all the items. The buyer refused to cancel the order saying I should have set my listing to prevented her combining postage which I don't think you can do with Simple Delivery.
I did ask her to cancel the order so I could then relist the items as combined lot with postage calculated accordingly but she refused saying I should have set my listing to prevented her combining postage. All my other experiences with buyers has been great and I've tried to give them a good service but I suppose not everyone plays fair. In my listing I had pointed out postage would be heavy due to the weight of the fabrics so feel I was upfront about the postage.