Have you had buyers/sellers back out of a deal?

Hi All,
Have you had a buyer or seller ever back out of a deal?
If so, would you please post your experience to this thread?
I don't know about you, but I've had this happen before and am WAY tired of the situation.

There are a LOT of RESPONSIBLE, REALLY nice folks on this site with good communication skills. And I've had, and I'm sure you too, have had some good experiences buying, selling, and just exchanging information.

But when someone makes an AGREEMENT to purchase or sell an item, and everything has been finalized, breaking/"changing their mind" to that agreement is called a BREACH or DEFAULT of contract.
At best, this wastes our time. At worst, we may have committed to sell a piece of gear to someone else in anticipation of getting the piece from the breached deal.

So what should we be able to do about this situation???

Did you know that this is NOT one of the FOUR situations that warrants negative feedback to be posted against someone's account here?!?

If you've had a similar thing happen to you, and would like to at least be able to post negative when/if it does, tell us about it please?
And also give your suggestions on what action could be taken (I'm sure this will get some interesting responses!) :-) to help keep this from happening in the future?

Thanks and Happy Listening!