Thanks for the replies. I didn't know auto-cancellation was an option.  Whenever I've had a NPB I've had to go through the resolution process and wait the 4 days for buyer to respond blah blah so was surprised to see I'd copped an unpaid strike with no warning.  If the seller had said they would prefer payment upfront and will hold on postage because auto-cancellation was enabled, fine. But they didn't. Also, I was the only bidder on all 3 of the first items and I think on all 3 of the second 3 items so it's not like they were losing out on all this money. 

Out of interest, I placed a manual bid on an item and it went through so no restriction. The 3 first items were combined as one order so maybe the unpaid item strike was against the single order and not 3 individual items? Maybe I have a bidding limit imposed? The items I'm bidding on tonight have a higher value. I have tried to find some more info but the Ebay rules regarding account limitations seem a little vague. I am hoping someone more knowledgeable than I can shed some light. Thanks