I personally wouldn't want to send a horse away on a trial... if an owner is willing to, all the power to them. The only time I was ever offered a horse on a trial was when there WAS something obviously wrong with the horse when I tried him out, but the owner wanted me to buy the horse, and said I could take him for a month and see if the problem resolved itself. (I sent the horse back at the end of the month
)
Too much can happen in a trial situation. I encouraged people to come out and ride the horse as much as they wanted, I gave them the option of coming out to a dirty horse out in the field so they could catch the horse themselves, groom it, tack it up, and warm it up themselves. I would have been more than willing to take them out on a trail ride with the horse if they wanted, but there is far too much liability in sending a horse away with someone on a trial - too much can happen. If the horse is under my care, I at least have some amount of control over what happens to them, besides the normal accident proneness of most horses. If someone was to take the horse on trial, and it were to come back lame, I would be out a lot of money, and with a lot of vet bills to deal with.
With the last mare I bought, I went out to ride her several times, and one of those times had the owner trailer the horse to another stable so I could try her out in an unfamiliar environment to see how she acted, but the owner was present and in control of how I handled the horse and what I did with her.
And the moral of my soapbox rant is - just because someone won't let you have a trial, doesn't mean they are hiding something.
And as far as drugged horses go - they are, as people said, "dopey" looking. Constantly looking asleep and relaxed - moreso than a normal laid back horse (droopy lips, ears not perked forward) and if it is a gelding - they will tend to drop. Especially if you are looking at a stallion, but for any male horse for that matter, if they are "exposing" themselves, looking droopy and listless, the warning bells should go off.
TCFC