This is how I explained the relist in my current auction:
This is a relist due to a fraudulent bidder ruining the first auction. For those of you who bid on this auction the first time, thank you for your interest and I apologize for the relist.
I had written it differently, but decided no need to give out more information than anyone cares to know. Just saying it was a fraudulent buyer most people understand (knowing Ebay!)
I was lucky, because it was something I was selling that was out of the ordinary for me, so I had saved the auction as a template (you can save up to 10 as templates) and I was able to go back and find it to relist.