Treat it as binding. The terms say it plainly: a bid is a promise to buy at that price if you win.
What actually follows from that is more useful than arguing about the word.
What happens if you win and do not pay
The window is 30 minutes — from when you first open the win for a timed auction, and at most 12 hours after it ended.
Then the win is cancelled, the item goes to the next bidder or back to the store, and it counts as a strike.
Three strikes inside ninety days pauses your bidding. What is a strike?
Nothing is charged to you and no debt is pursued. The cost is the mark and the item — which is a real cost, because a paused account cannot bid on the thing it actually wanted.
The one way out
Ask for the strike to be removed, if there was a reason. The cancellation message says so itself. A failed card, a lost phone, a week in hospital — these are lifted, and more often than people expect. Can I appeal a decision?
What is not a reason: changing your mind.
Can you take a bid back?
In limited circumstances, and it is not something to rely on. Assume you cannot. Can I take back a bid?
Why it has to work this way
Because the seller gave up the item. For the minutes your bid stood, nobody else could win it — and an auction where the winner can walk away costs the seller their evening and the under-bidder their chance.
That is also why the under-bidder gets a second-chance offer when it happens. What is an under-bidder?
The practical reading
Do not bid to see what happens. Bid at a number you would be content to pay right now.
Decide your ceiling before the item comes up, because the last ten seconds are not when judgement is at its best. The last ten seconds
Have a working payment method ready. Most unpaid wins are a card problem, not a change of heart. My payment failed
For sellers
The promise is what makes the format work, which is why shill bidding is treated so seriously — bidding on your own items corrupts the one thing everybody is relying on. How do I know the price is fair?
More: what happens if I do not pay, what is an unpaid win, how bidding works.