If you do not pay for the item, your seller can open an Unpaid Item Dispute. This will give him back the fees he paid when you indicated that you would purchase (never thought of that did you?), prevent you from leaving feedback, and put a Strike on your account.
Many, perhaps most, sellers have automatic Blocks against bidders with Strikes, so it will be more difficult to bid and buy in future, In addition “too many” strikes will lead to eBay closing your account.
