As a buyer, you can cancel them sometimes. I had an instance purchasing as a seller recently where I saw an item I wanted for around 100$, which isn't a terrible price. I was going to offer 85$, not insulting but would save a little. Then the ebay prompt popped up and said to offer 45$ as this would have the most luck of a response. I found it really weird and also a little unfair to the buyer, but figured the system must calculate that is what the buyer will accept. The buyer didn't answer at all and after a day I found one locally for around 80$ and cancelled the offer. I felt a little embarrassed to even offer it because it was a lowball and I normally wouldn't offer an insulting figure like that for something worth more.

Then, recently when I am selling, I find that ebay automatically turns on the "offer" feature and usually makes it really low so I get extreme lowball offers until I turn the function off (Offers all day like oh I will give you 70$ for a 2020 macbook lol)..