You can't cancel as a buyer, you can only request that the seller cancel the transaction.
Be very polite, and don't mention the reviews.
When you receive a notice about the cancellation, agree immediately.
You can leave feedback, but if this all goes smoothly there is no reason to.
I'd nag and say you should have read the WHOLE listing before bidding, but you've figured that out.
The alternative is to not pay.
The seller could then open an Unpaid Item Dispute. You would get a deadbeat Strike which would make it harder for you to bid on eBay because many, if not most, sellers automatically Block bids from deadbeats.
