I've just had a look at their rules: http://pages.ebay.co.uk/help/policies/accepted-payments-policy.html "Sellers may accept COC (cash on collection) or cash in person transactions." "Sellers may not solicit buyers to mail cash. Sellers may not ask buyers to send cash through instant money transfer services (non-bank, point-to-point cash transfers) such as Western Union or Moneygram." I wonder if they're having an issue with listings that don't make this distinction clear.
Sucking his keyboard for inspiration, platypus typed: Sounds like that's what I fell foul of. But they removed it within a couple of minutes, before it had even reached the search pages, so I very much doubt if it was reported by a user.