Always err on the side of caution.
I think it all depends on what you are looking at and your level of handiness. Your experience and research. It also helps to have a good handle on feeling out people and assessing whether they are genuine which also comes with experience.
Maybe we have been lucky - or maybe it is our own expectations of what we are buying in the first place.
As far as airstreams go - there has not been a single one (except the wrecked 99 that was within a 1000 miles and a different country no less.
For our first - a gentleman from here befriended us and helped us out with the sale and purchase of our 69 GT.
How that worked was - lots of initial research on buying our first vintage. Knowing what to look for and scouring a ton of pictures and lots of posts here at the forums. You get to know the people here too on their own levels of understanding and experience.
When all our questions were satisfied with both parties and our own needs for a particular trailer we set the logistics into place - but with safeguards.
We had our airforum new friend go and inspect the trailer and give his full report - more questions and lots of photos and we were okay with what we were purchasing.
Next we sent settled on a price with the seller and required deposit. Then we sent the deposit to the inspector - who exchanged that for the title but left the trailer with the seller. We had the title searched and were satisfied we would be able to bring her across the border.
We then sent the rest of the money though to the inspector and he picked up the trailer. When we arrived we had made one last concession and if it did not work out it would all be reversed. We got together with the owner to do the final bill of sale and the remaining funds.
It all worked out like clock work.
Our GT63 was an ebay purchase - but I spent a lot of time with the seller to feel him out. There were a few little hiccups but nothing we could not handle. The trailer inside was a grotesque mess - but we knew that going in - we were basically purchasing a shell and that is what we paid for.
Our CCD purchase was through a Silver Sister friend here on the forums - so we had already met, I had already seen the trailer several years before I had purchased it. It also had a few unfortunate hiccups with some panel damage - but nothing that would make me back out of the sale. I was on the hunt for a specific model and year and she had it ha so I was going to get it. This one turned out to be the best decision of my life. I love it and I have put 1000's of miles on her and many more to come.
So like I said - if you are not a handy person at all you might want to stick closer to home and even pay the extra money to go through a dealer.
If you are like many of us here - a bargain is a bargain at any cost
How else are you going to save enough money to travel with it
Or buy that TV.