How much time have you invested in evaluating this horse so far? I agree with the others that a simple “Thanks so much!” is sufficient—honestly, you don’t even need to tell me that it’s not right for you. But it’s when a buyer asks me three million questions or has a bunch of special requests just for the heck of it that I get annoyed.
I have a very, very nice young hunter for sale and just spent days entertaining a buyer who I felt was quite serious. I took pretty extensive additional video of the horse for her, as she’d be buying off video, disclosed all exams and X-rays, and so on, only to be told, “Sorry, I’m actually not looking to buy for another two or three months.”
Or the best: they know the price, proceed to ask 20 questions, then say, “Sorry, over budget!”