Always a good idea, they might pick up on small important things that you might not both on and off the horse. If they can't come in person then I'd video my ride on the horse I'm trying and takes tons of photos to show them later.
Yes, if you are inexperienced and if its your first horse. If you don't know what to look for then your trainer can help you ALOT. I would also have a vet go with you if have your own personal vet(not really necessary). So it really depends on your experience. :)
Hope this helped!!