You need to read the fine print above the button to place a bid/offer (and any additional confirmation/change screen after you press the button) to see if you are pre-authorizing automatic payment.
eBay had been "experimenting" with requiring pre-authorization of payment for Best Offers for over a year and a half (started prior to Halloween 2021), adding more and more users into the test group required to do so (sellers can opt their listings out of it which some do who depend on attracting buyers by offering a discount for combined shipping). Too many users were making offers and then not paying when it was accepted, and too many of those were scammers who would try to get the seller to text or email them to get their number/email address to send fake payment messages to. In Fall 2023 they made it permanent and all buyers are now required to pre-authorize automatic payment for Best Offers they make on listings for sellers who have not opted out of the program.
They started trying it out on auction bids (with a smaller group of buyers that is growing) in Spring or early Summer 2023 and that is ongoing with more and more (but still not all) auctions and bidders becoming subject to it.
They added the 1 hour window to manually checkout this Spring to cover some issues, though it covers the issue that not all payment methods available at checkout work with pre-authorization a lot better than the issue with combined shipping. In Fall 2024 they started testing allowing 7 days to manually checkout in some circumstances to facilitate combined shipping
Outside the 7 day test, they are still leaving it up to the seller to either opt out of the pre-authorization requirement or do partial refunds or just not combine shipping (which has always been an option so don't assume that the seller will give a discount for combined shipping). Look for sellers who address combined shipping in the description and/or whose items don't require pre-authorization (if you don't get a confirm screen requiring a shipping address and payment method then either that seller has opted out or eBay is not including that auction in the test for some reason only eBay knows). Or message the seller and ask about it--often they have no idea this is an issue because eBay opted ALL sellers into the requirement without much notice.
