Okay, I understand completely why you are seriously angry, but I don't think you should just quietly seethe or 'move on'.
There is a middle ground between doing nothing and going ballistic.
What I'd be doing is writing a polite message. Polite in that you don't go calling the person a jerk or making any comment about their character, much as you might like to (and be entitled to, actually).
Put the emphasis on yourself and how you feel. Disappointed, seriously let down and financially affected. Outline the basic facts of what you did in good faith for them, step by step.
Mention it is the biggest thing you have done for someone.
Make no demands. Just leave it at that. Phrase it as advice for the future, just so they are aware.
People can often make excuses for their own behaviour and they can gloss over in their mind how it could have any effect on the other person. We see that all the time here in posts where buyers haven't always really understood why sellers weren't happy to just cancel at the drop of a hat etc. They didn't realise what extra work they put sellers to (I know that aspect is changing in ebay now, but talking about in the past)
If you abuse them, they can then wipe it further from their minds with the justification of-well, I am glad I didn't buy from them anyway as they weren't very nice. I did apologise, after all.
But if you couch it in terms of youself, they can't argue with that.
And although we can't change people's behaviour, outlining just how you have been affected, step by step, may in fact give them pause. They may have no idea it was any big deal to you.
I have been in similar situations (not with commercial transactions but in the workplace) Once was with a student teacher and one day she let me down badly. She arrived 15 minutes late after school began on a day when we were going on an excursion. The other buses had gone and there I was, waiting with parents and another class, we had all been ready for 30 minutes. The student teacher had no reason for running late, no car trouble etc. No message sent earlier. She just walked in and gave an airy sorry.
I kept my temper but later in private outlined exactly how it had affected me and why it wasn't on. She ended up in tears but I didn't particularly care. She got the message-that sorry didn't cut it, that it was more of a big deal than she thought. I doubt she would ever do it again to someone, put it that way. I failed her. I was glad to get it off my chest too, even though it didn't change the situation.
You deserve your say, say it. Not wasted time at all. Won't fix the problem but your buyer will know they have been a jerk. You won't have to tell them.
