As a purchaser, it is exciting to have the ability to go on-line and have a whole new market of available horses for your selection. Isn't it great!
Based on my own experiences, I think the extent to which a seller will go to present their horse to a potential purchaser is different based on several factors. Specifically breed and price range.
We have purchased 3 horses without seeing them "in-person". Two were from a reputable breeder and the other was from a trainer who competes successfully at national level.
Each offered comprehensive videos, health/soundness certificates and guarantees and client references. Needless to say, these horses were not priced in the inexpensive category.
However, regardless of the price, you should feel comfortable in asking the seller to provide any amount of information you desire to determine whether the horse is one that you want to spend your money on and live with everyday. Consider asking for the name and telephone number of the horses breeder, trainer, vet, farrier and previous owner, if applicable. Ask how long has the horse been on the market. If they are reluctant to provide specific information there may be a reason for it. Be sure to pay attention to the sellers facilities when you are there. The manner in which they maintain their barn and equipment, the quality of their feed, etc. is indicative of the treatment that they provide their animals. If it is dirty and poorly maintained, you can probably assume they have given the same treatment to the horse even though it might be presented to you clean, groomed and "show-shined" up for the day.
Ask them to do everything that you will want to be doing with the horse before you do it yourself. This gives you time to watch how they handle the horse and how it rides.
The road trip idea is a great one. If you find a prospect, try to spend as much time as possible with it. Go back the next day and do it all again if you have the luxury of time to do that. Before plunking down the cash be sure to ask for a 3rd party vet check and a satisfaction guarantee.
There are lots of great articles and books that will give you some guidelines when making a purchase. You can also source lots of good advice on various internet sites so that you can make your own pre-purchase check list. This will really help you when it comes down to making comparisons on several horses which you might like.
Above all, be pragmatic, set your emotions aside and take your helmet along with you. I laugh when I think about all the times over the years I have ridden a horse that a seller has told me "this horses never bucks"......right.