Hi Lily 🙂
You have to know the Market, consider the demand for this kind of horses. When you make an offer on a horse, be prepared to start the negotiation process. It’s always possible that a seller will agree to your offer, but it’s more likely that they’ll propose a higher price or reject the offer entirely.
You have to be realistic, and to be ready to leave if the price is not what you want!
I just read this article about it: http://www.chronofhorse.com/article/etiquette-horse-shopping-making-reasonable-offer
There's the point of view of the buyer but also of the seller so it's really interesting! You also have a lof of advice, of things to do or not.
Here's an example:
"DO: Quickly prepare an offer for a horse you’re sure about—time is often of the essence.
DON’T: Waste time negotiating while others could be readying an offer superior to yours."
First of all, you need to know if the price is firm or not, so that you don't waste your time nor the seller's time.
If the seller is willing to negotiate, then you have to know if the price of the horse is realistic or not. Check out the price of other horses with the same capacity, age, breed,...
You can discuss the price by telling the seller what you don't like in the horse, and by telling that you can buy the horse quickly, if the seller wants to sell the horse quickly, it will help.
Hope it helps 🙂