Ebay Promotional postage rule

Today I removed the Ebay Promotional postage rule, witch I was using since I have my Ebay shop. I had one rule for all listings.
Spend more than 20GBP on 2 or more items and get free shipping. The last time I just cancelled the order because buyer didn't read the offer rules. This last time I lost my money on two items, because, again, buyer didn't understand the rules. As this time it was a returning customer who bought from me in the past, I made an exception. The promotional postage rule is for ITEM PRICE ONLY, not for price+ shipping.
Buyer bought 2 items. Price per items + shipping was 24GBP. I waited for payment, and got email, asking why do I have to pay for shipping for 2 items, the total is 24 and I think there is free shipping when I spend 20GBP. I messaged back and told that the rule is only for item price not for total. I offered her to pay the shipping price for the heavier item only. There were no answer so I contacted a buyer again and send a new invoice without shipping price and told as shi is a returning customer the shipping will be on me this time. She paid in 2 minutes.
The buyer paid GBP13.50, Ebay fees are 1.62, Paypal fees was GBP0.73, the cost of two items was GBP2.42. Shipping is BGP10,34
13.50-1.62-0.73-2.42-10.34=-1.62
I am done with this promotion thing, because people do not read, they just see what they want to see!!!