Are you forced to buy something you've won on Ebay?

[Dyils]

Hey guys,

My question is simple - Are you legally bound to pay for an auction you've won on Ebay? And more specifically for the UK.
The reason I'm asking is because I'm looking for the best deal possible on a certain item, but because all auctions end at a different time, I want to bid on several of them and choose the best bargain at the end. I know it's inconveniencing for the sellers, but as an international student, I have to try to get the best possible deal. And if in this case I'm not bound legally to buy it, then what about when a seller explicitly states in the description that the winner must buy the item?

An answers will be much appreciated.
"Yes. After winning an auction, if you do not render payment, you will be banned from eBay."

And if I pay in cash upon collection of the item? Or should I refrain from doing that?