Bid or buy double standards

I had recently put an old laptop on bid. I had set the shipping costs to the lower value of what I found from other sellers. I had bidders who changed the value upon placing the order and complained about the shipping cost. It's really simple. If you are unhappy with the shipping cost then don't place an order or discuss it first as bid or buy charges you when an order is placed regardless of whether the buyer pays or not (absolutely stupid). I had to wait two weeks to try and get the costs reversed and one of the buyers denied that he didn't want to pay. I had to then call in and ask them how can I show them proof as I want these costs reversed. I was then told that my shipping costs are too high which was *******. There were sellers with higher costs than myself. It was completely unfair. Why were they not warned about their costs? The whole process at bid or buy does not assist the sellers. Don't use the service. Rather use another platform.