Probably there is no good way to generalize, as every seller (and buyer) are different. Really, it's up to the seller in a way.
I've bought many things from a distance and there are oftentimes some obvious clues as to how it might go in the ad (although some sellers will surprise you if you take the time to check further). It's great if there are good photos, and good communication about features, questions, etc. On the other hand for one reason or another, some sellers just aren't interested or able to help a distant buyer. No photos, little information, etc. Maybe they don't know how to do e-mail/web/photos. Maybe they don't want to. Or maybe they just can't imagine it. I've had responses such as "Oh, you don't want to travel that far just for a boat/car/etc.." (Au contraire, but they can't imagine that.)
Some folks totally get it and are dreamy to work with. Photos and info flow, and they may understand/trust enough to hold a boat/car/etc. for you - either with a deposit, or in the "I'm leaving the house now, I'll be there in twelve hours, will you hold it so that I at least know it will be there when I arrive" way. It can be easy peasy these days, with e-mail, .jpgs, PayPal, etc. But it does take a certain willingness by the seller and follow-through from the buyer.
I've found it helpful to ask about certain things in advance just so we are all on the same page. Things like "is it the first person who shows up with cash, or are you keeping a list, or is it mine until I get there if I send you a deposit, or?" etc. Sometimes people (very understandably) haven't really thought it through in advance. And as Aurelia mentioned, sometimes it's more than just "first cash." Sometimes finding a good home for something is just as (or more) important.
At any rate, there are as many scenarios as there are buyers and sellers. A friend of mine once drove ten hours to buy a pristine truck only to arrive and find it had been rolled! As if he either wouldn't notice, or would be, "well, I've driven ten hours, so I guess I'll buy it even though it is nothing like you described" (um... no). On the other hand, I bought a rowboat one winter that was halfway across the country. I sent a check for the full amount (perfectly comfortable sight unseen due to photos and comms) and the owners kept it in their boat barn until spring, then suggested we plan to stay at their place (in a historical location on the coast) for a few days and make a mini-vacation of it. One night we had a lobster dinner capped off by a lovely sunset row together on the bay - us in my new-to-me boat and them in the even nicer boat that was taking its place. Good times.