A few years ago, I had a similar issue with a buyer who kept buying my items and paying with e-cheque via Paypal.

The e-cheques would always, always bounce 7 days later. And then she'd try sending another one. At the time, you could not open an UID while an e-cheque was pending.

She used two different surnames but the same address over 5 different accounts. She drove me crazy and in the end I'd just relist the item the moment she'd "buy" it, as I knew payment would inevitably bounce 7 days later. eBay gave me permission to cancel her purchases without penalty and said they'd remove any feedback from her, but they were SO reluctant to ban her from the site it was beyond belief.

Thank God she eventually gave up when I just kept cancelling anything she bought within minutes of her buying.