Well I do breed with the intent to sell and to make money. I don't think there is anything wrong with that. People that don't want to, don't! But hate to say it, if there weren't "breeders" out there willing to sell there wouldn't be horses for you to own!
As for vetting a buyer. You can ask a bazillion questions, have an iron-clad contract and still have them end up in a bad position. I had that happen to someone with 30+ years horse experience, animals lover (found our = horder), etc., seemed ideal until I had to take back seven of them last Fall that were in starvation, untrimmed, thrush mode. Fooled me good.
When people inquire about a horse or owning one, I do ask what they're wanting to do with it? Family pet, show, breed, etc. The ones that want to breed are the ones I quiz the most. So many have been lied to about how easy it is, and all the money they'll make, etc. Plus if they don't believe in registering or maintaining a herd, I'm not going to contribute to another "let's try it and we can experience birth" opportunity.
The red flags for me.
1. I can't really afford to buy one (or wanting to make payments on a horse $500, etc.). Well you won't be able to afford to keep it, as the purchase is much less than keeping a mini long term.
2. It's going to be a pet, but I want a mare in case I want to breed. Quality counts and a bad quality horse costs just the same to keep as a high quality one.
3. They complain about past purchases and have never had one Mini work out. Who'd they buy from, what are their expectation and why aren't the being met?
4. I want a mare and stallion so we can try breeding. Eek! Do some research, educate yourself on stallion management, foaling issues, etc.
Other considerations:
Do they have a farrier/vet?
Do they plan to follow through with registration?
Do they have time to spend with a Mini or is it going to be dumped in a stall/field by itself? If they don't have time, get two at least they have company.
I had a woman show up here one time with her trailer, then every time the Minis got near her she'd swat at them. I was thinking you do NOT need to own one of my horses. She finally left, not happy but she was not a good home. Another person I refuse to sell to is on MTV with his Mini, I didn't like what he wanted to do at the time (not good promotion of the breed IMHO), so refused to sell to him. Someone did, more power to them, not my cup of tea.
Overall, I've had fairly good luck with sales over the years. Most of the people do stay in contact and I tell ALL of them there are no stupid questions, please call/email I'd rather see if I can help than find out you spent $$$ on something that could have been dealt with easily or the horse died. I also encourage people that buy, if the cannot keep the horse for whatever reason to please contact me, I may be able to take it back/buy it back or at least help rehome it.
End of the day communication is the key.