OK, thanks - I'm going to hold off for the moment, until I get an official response from eBay. I asked them last night, but just received a stock reply about paying via PayPal, so I've repeated the question and will wait to hear what they say. Will hopefully get a more personal response next time.

I've also made a request to the seller asking them if it's possible to cancel the sale, as I believe this is possible as long as you request it while the item is still active (it's a BuyItNow with more than 10 items available, so it's still ongoing). As yet, I've received no reply from the seller.

It annoys me that the seller wasn't upfront about the fact the PayPal purchases weren't made directly from the PayPal site, but from a third party site. If I'd known about this beforehand, I wouldn't have bidded for it.

I'm just so cautious about entering my PayPal account details on anywhere other than the official PayPal site.
Anyway, thanks for the advice.