Green riders often/usually want to take a horse “on trial”. Fair enough I guess, from their point of view. But keep in mind that with many horses, especially greener or inexperienced horses, the first few days or even weeks at a new home, the horse may not be “himself”, not settled in yet, and making a judgement in the first few days may not be fair to the horse (or to yourself). If you are looking to buy a horse who has “been there and done that” and think that you have found one offered for sale, he should be fine on a trial, settle in quickly, and show his true colours. But keep in mind that his behaviour and performance may not stay the same if the level of riding and training, care and happiness is not maintained adequately in the new situation. If a seller is representing a horse as that sort of horse, a trial may be agreeable, and may go well, but it is not guaranteed to continue to go well. But if the horse is inexperienced with going places and different things, the seller may feel that the horse may not be suitable for a person who is needing a “trial”. Experienced riders and buyers like what they see at the home barn, and know that they can deal with whatever happens at the new facility, taking into consideration the quirks that a horse may exhibit when he changes barns, and is OK with giving a horse time to adjust to new surroundings and new ways of riding, and new or different things being asked of the horse. He’s buying a horse, not a guarantee. Green buyers are looking for a guarantee, and, of course, there aren’t any.
The risk of injury to the horse when sending a horse off on trial with someone the seller does not know well (or at all), is a pretty scary situation for the seller. Just about as scary as buying a horse without a trial period may be for a buyer. And yes, there’s always insurance possible, adding costs to the transaction. But money does not always make bad things better, if bad things happen. Both buyer and seller are taking risks when they take a horse on trial, with a buying/selling transaction “incomplete”.
I have never asked for a “trial” when buying a horse, and RARELY give a trial when selling one (I can think of only one time). If someone wants to pull blood on a horse I’m selling in case I have “drugged” it when they came to ride it, go ahead! Please do, if you are the sort of person who is looking for someone to blame if it doesn’t work out as you had hoped.