After a while, you will learn, and get so you don't get involved in these sort of situations any more, and then you will feel better.
As Doctor Phil would say, 'So...how's that workin' for ya'? You gonna hang around some more, and have more of the same things happen, and have more of the same feelings?
This is the first website where I've seen these sorts of complaints, that they wanted to buy a horse(or other stock) from someone I did a favor for, but the horse sold to someone else (often at auction) for less money.
I'm going to just take a swag and say the situation looks very different to the seller. I even would say, in the same situation, MOST sellers aren't going to like all this, 'I'll buy it when' or 'I like that one but I want to....'.
'I'll buy that horse for X if he doesn't sell at the auction' sounds a lot more like, 'I'm hanging around to get a favor and a cheap horse - I talk about wanting to buy something all the time, but I always have an excuse why I have to wait. And....after you come home from the auction and are desperate and miserable, because you didn't make your target prices, or your minimums and have a bunch that didn't even sell I'm going to start dickering and dealing and have you right where I want you, and you'll have to give me what I want because I'm your 'Friend' and I do stuff here'.
If you want to buy an animal, what you need to do is buy it NOW, when it is for sale, at the farm. Not when the sun trines Jupiter, after the auction, after the High Holy Days or Wal Pershnock, on a Thursday when the stars align. Just BUY IT. Say, 'I'll give you X for Daisy TODAY, RIGHT NOW'. And the owner may say, 'No, I want Y' and you come back and say, 'how about X plus Z', and the owner says 'Done'. You pay cash for the animal, and take it to your house, and put it in your barn.
It works out a whole lot better that way.
I'd also say, it is really, really, really, not a good idea to 'hang around' and 'do favors' and 'help out', and then think to yourself, 'well now I'm going to say what I want and I should get it'.
People lose respect for people that do that - very, very quickly.
When you are ready to buy, show up with your money, deal, and buy the animal. Otherwise, stay home.
Nothing else really works quite as well.