What i would suggest to those who received an unpaid item strike after a refund, to file a complaint with eBay.
It is under the eBay policy to remove the strike filed by sellers if you can provide proof of payments, email communications (eg refund), etc.
http://pages.ebay.com/help/tp/appeal-upi.html
Don't let the sellers get away with it. Your accounts might also be suspended if you receive too many strikes.