I know you won't care, but I think it's sad you have this attitude.
It sounds to me like your word doesn't mean anything.
I would have to have an incredibly exigent circumstance to cancel at the last second, and even then, I likely wouldn't, as when I give my word, it's as good as pledging my life.
The funny thing is, that I DO care. I care about my reputation. I care about my word, very much. I believe myself to be an honest man, more honest than most even. And I knew I'd get pushback. But it's a dynamic world.
As far as "incredibly exigent circumstance," things happen. Story time.
I went to privately buy a car once off of a newspaper classified (when people still did that), agreed to the purchase, and the car literally dumped its' coolant on the road just before money changed hands. Yeah...no. The situation changed. If it happened half an hour later I would have been unhappy but wouldn't be trying to go back on the deal. The seller was unhappy and tried to BS me that it wasn't a big deal as a green puddle formed on the parking lot.
I agreed to sell an extension ladder when moving out of my old house. $100 agreed to (a serious bargain, I think). The slimy bugger brought $75 after texting me over and over to make sure I didn't sell it to someone else. I said hell no. He magically came up with the full amount. I still said "hell, no." Sold it shortly after to one of several other people who had been texting me about it.
I went to sell a car (privately) and the buyer kept delaying, changing the time to meet, and being a pain in the ass. So I sold it to someone else after a few days. I told him I was going to if he didn't step up. He accused me of not honoring my word, too. Screw him. I didn't feel obligated to be strung along until he could (or not) finally get things organized.
I sold my old boat (privately). The buyers financing fell through (we agreed on a grand for Christmas Sake) and he had to back out. Sucks, but life happens. I wasn't mad at him for it. I was annoyed. I sold it to someone else later that week for $1,200, so good for me.
I almost sold a gun to someone 25 or more years ago (not in Maryland). A friend of a friend. Met him at a party, he seemed ok. He wanted a budget gun, I wanted to upgrade, so we made a deal. Met the dude later at his place. I got bad feelings about things. Backed out. Eventually traded it in at a gunstore for a sweet used S&W 6906 for something like half what the guy was offering. I don't feel bad about that at all. The friend eventually told me that the guy was a real dick and should never be trusted. Gut won.
I pulled out of another deal (rifle) when my Father died. Life got chaotic. Seller understood. I felt bad, but my priorities where clear. I suppose if the seller made a stink I would have found the time to finish the deal, but he was pretty cool about the whole thing.
I've lived a long enough life now that I've accumulated a lot of stories. Surely many more than listed here, although these are all that come to mind right now. Rarely are things black and white. Things happen. Reasonable people understand. Sometimes feelings get hurt. We try our best. What else can we do?
For what it is worth, I've agreed to sell stuff, gotten a better offer, and did not back out of an agreed deal for a few more bucks. Not the way I role.
If there is a history of repeated unethical behavior, I can understand being upset. But sometimes things change.
In the end, until the money moves it doesn't really count. Hell, I've bought things retail online, been later told the product was backordered, and eventually had the order canceled. This isn't even that uncommon. So don't count chickens, and all that stuff.