a buyer should confirm combined postage rates/costs before buying multiple items.

On another ID I had a buyer hit the Buy-Now button on two items.  One had free postage and the other had 500g satchel cost postage.  I had a line in my listings that "I do combine postage" and they messaged me to let me know that they expected the invoice to show free postage for combined postage.  I changed the line to clarify exactly what combined postage meant.

I think that buyers can have a skewed idea of the intricacies of selling and I recommend to all those who have been buyers only to give selling a try.  Sell just one or two small items.  It gives a totally different perspective to the eBaying experience and what sellers go through.