Yes, I have had sold items relisted. The last time was recently when I discovered an item was listed that I sold when I started selling around 2 years ago. It was only sheer luck that I noticed it. I have also had it happen previously a few times. The only reason I found out the first time was because someone bought the item and I knew I'd previously sold it. Thankfully the buyer was understanding.

Now, I check my listings every Sunday to make sure there are no rogue listings appearing.