The only trials I see these days are lease to own deals where your lease fee goes towards the purchase price of the horse but is 100% non-refundable.
I recently purchased* two new horses more or less on the same day. I posted an ISO ad in my (very horsey) area with specific criteria and a very reasonable budget for the ask. I had about 20 replies within the first few hours and by the end of the day, I’d made 3 days worth of appointments to see my top 6 contenders. I knew within 5 minutes of sitting on the first horse that he was the one, but I kept an appointment to see the second one because his video was extremely promising. I was not disappointed with horse number 2 and decided that I was going to bite the bullet and vet both. I did not put down a deposit on either though I offered as I was able to book vettings within 24 hours. Findings on horse one were on par with a horse of his age and experience level and I signed the check and the bill of sale at the clinic. Findings on horse two were very unexpected and while it didn’t put him out of contention, I had a very frank conversation with the owner and ended up having a 120 day “out” contract if a specific intervention that was deemed necessary either a) failed or b) caused significant behavioral changes (hence the asterisk). I would not recoup any of my costs to care for him or provide this intervention, but she would hold my check and I could return him at any point within those 120 days and get my check back. Very, very unusual but then again so was the situation. We’re about halfway through the contractual period and so far, so good, so I’m very hopeful.
In a nutshell, know your budget, have a vet in mind (particularly if you’re looking in an area outside of your home base), and be prepared to move on the horse quickly. The horse we bought almost immediately met a very specific niche (dead quiet, puppy dog personality, happy to do the x-rail job, but competitive at the 3’ level in all three rings to go to a forever home) and I knew the farm he was from and the reputation of the trainer so I had zero questions about suitability and his show record spoke for itself. The second horse was a total wildcard that piqued my interest solely based on breeding and I was gobsmacked by the video. Total freak of nature and an obscene amount of raw talent. I had no need to see either horse twice, but the offer stood with both owners if I wanted to try either a second time. You may or may not find this to be true.
Good luck, it’s a wild shopping world out there!!