As others have said, information is your friend. The horse market is variable depending on the location, the breed and the discipline. Training adds to the price of a horse, so if you are looking for a well trained horse with a show record or experience, then be prepared that the horse’s price will reflect that training. It cost money to put it there.
The clearer you can be on what kind of horse you want, the better. The more research you can do about what horses are available in your location, the better an idea you will have of what that horse’s fair market value will be. I agree that it is unwise to look at horses priced at $$$$$ if you only can pay $$$$. While there always stories about someone getting a perfectly trained horse for a song, that is uncommon and unlikely to happen to you.
I sell horses from my own program as well as consignments. I sell a particular breed that is not in ready supply and has a demand that is far stronger than the existing supply. I also own my own farm, all the horses are low maintenance, and they all live out 24/7, so keeping a horse on the market is not a big deal for me. Some sellers are very motivated; I’m more take it or leave it. I actually have had owners who consigned absolutely refuse to take a penny less than the asking price. I’m not always that inflexible, but I don’t sell low because I always have another buyer. I’m also not a jerk; I had one buyer trying a horse when I got another call from a second buyer wanting to buy that horse sight unseen for $500 more than the asking price and no PPE. I said no, that she had to wait in line behind the buyer who was trying him (and who did buy him.)
We agree on the price before the PPE. If the buyer does no like the PPE results, then there is no sale. It’s not a negotiating point. I have had one PPE vet say a horse is slightly off on the lunge line and the next week another PPE vet say the horse is quite sound. (The horse has been sound to this day.) In the first buyer’s case, I said that she should talk to the vet but if there was any uncertainty, she should pass on the horse. She did and that was fine with me. As I said, there was a line of buyers for the horse and a vet who was happy with the performance on a lunge line and took x-rays showing the horse had no issues.
As others has pointed out, there are some sales related costs that may be covered by the seller. I always provide the Coggins and will get a health certificate. I will keep the horse on my farm at no charge and coordinate with a shipper. If the buyer is close by, I may be willing to haul the horse there myself at no charge. I do cover the registration transfer fees and make sure registration is transferred. All horses are sold are current on shots, worming, trims and floats. I throw in a new halter and rope. So you might be able to negotiate some extras.