I buy and sell horses all the time... I also get lent horses to use for a while, and give them back once I don't have a sue for them. I've had about 5 horses in the last two years!
I love each and every one of them, BUT if I'm not using them, I think it's cruel to hold on to them when they could be out there with someone who will love them every bit as much as I do, and ride them all the time, and give them the work they deserve. My passion is training... Helping a horse who has been ruined/traumatised/not educated become something that someone can enjoy and love. To do this, I have to sell horses.
My first pony was an 11h Welsh mare. She was a cow! She taught me hopw to stay on through just about anything. But, there was no way I could have kept riding her! I just got too big, and I learnt all I could from her. So I sold her. She had a baby, who shows successfully, and now packs around other little kids with much better behaviour than she had when I got her. To me, that was a win/win situation.
If I don't sell horses, I can never progress, and I never want to stop progressing. New problems to solve, new obstacles to overcome, new heights of performance to reach... I'm always aiming for more. I have ONE forever horse, my boy Wildey, but I do realise that I have learnt all I can from him. So I let other people learn on him, There are two girlsat the moment pleasure riding him and learning a whole bunch doing it, and another lady rides him at MGA competitions, and he is teaching her loads. I am always present when people are riding him, as I know him inside out, and it makes for new refreshing work for Wildey, a great oppurtunity for the kids who ride him that can't afford a horse, and my peice of mind that I will always have a say in how he is treated and where he will end up.
Apart from him, I enjoy the challenge of getting a new horse, and making something of it. I bought an ASH gelding for 2k when he was 4, and borught him up to A grade jumping, and was told he had the potential to make 1* in less than a year if I campaigned him at open events. I am not into eventing, at least not open level, so I sold him on to a girl who wants to go up through the grades in eventing, for 6k. The profit allowed me to buy a well bred prospect fior my next horse, which is Bundy. He has amazing potential for a lot fo things, and I think he may be my favourite horse ever apart from Wildey, he has such a cool mind, yet I know that I will eventually sell him, to allow someone else to have the joy of riding and competitng this amazing horse. I do think he is the best horse I have owned, potential wise. And the profit from Vodka allowed me to buy him, and so on and so forth. I want to keep learning, and new horses allows me to acheive this.
That being said, I ALWAYS make sure horses I sell go to good homes, and maintin contact with the new owners.
I've taken two ponies on lease/lend agreements... One the owner did not have the heart to sell him but wasn;t usign him... So I took and and trained him up to be a really handy games pony, and a kid safe pony. The other was a family friends pony who wasn't being used, and again, I put the work into him to make a decent games pony, and a kid safe horse, and a definite show prospect, then gave him back.