This happened when I bought my best mare. They had someone come look at her from Hawaii....which was a long trip. Person was hung up on x-rays for a 14 year old upper level jumper and offered them 4k less than asking price. I flew out the next weekend with a check for full price and no contingencies about the vetting (since I wanted to breed her not ride her) and got the mare. I feel badly for the other buyer, but I have had it happen to me as well and just moved on and found something just as good later. Once you find something you like, you have to assess how much it is worth to you and then fork it over, or else you risk losing it when someone with a better offer (or who is more decisive about what they want) comes along.
Horses are a business...no other industry is going to keep something on hold for you just because you come to see it or ask a lot of questions about it. Even holding after you express clear purchase intent and before you fork over the money is a courtesy, imo and certainly not a requirement.
Several years ago I had a VERY nice yearling for sale. A local "buyer" had come out with her daughter to see him SIX times. Then she negotiated a lower (quite a bit lower) selling price which I agreed to because I had a temporary cash flow issue... And then she says she's not ready to buy....
Months go by and an out of state buyer pops up. Seems really interested and asks for a video, which I send. She says she wants to see him in person.
Buyer A shows up again and wants to buy now, but I tell her that the negotiated price is no longer valid. She says, "well, if all you care about is money.... "
Out of state buyer comes to see the horse and immediately puts down a deposit and after horse passes vet check, purchases at a price much closer to what I originally wanted for the horse.
This is the way it goes. If you really like a horse, don't expect the breeder to hang on to it for you unless you put some money down.