This is a private sale not a public auction.
I have no objection at all if I won a bid and seller tells me
sorry he changed his mind or he does not want to sell to me (I will not insist he tell the reason why) and prefer to sell to some one else;
Whether he sells more cheaply or more expensively to other buyer is not the issue. It is not significant.
Likewise buyers can back out at last minute and say sorry I do not wish to buy now. Maybe something happened and he needs to money for something else. It is not for the seller to insist on a reason why or pry into buyer's financial situation.
Maybe the condition of the item is not what he had in mind though the seller had put a "7" rating to it. We all have different ideas what a "7 out of 10 points" condition should be.
CS is just a useful facilitator of possible potential transactions.
It is not a law court enforcing sales or bids.
Also it is possivle to use CS bids in a bad way to ramp up bids and up prices in a concerted pre-meditated way to fool unwary buyers.
i.e. bidders A, B and C and all "kaki lang" in a scam to up prices to unreasonable levels until genuine buyer D comes along and bids higher than C. If there is no bidder "D' then a fake "sale" is made to C. :bsmilie: