I bought the GN I have now off eBay in 2006. Flew to NJ and drove it right back to Memphis, TN. Great trip so, in general, yeah, I trust them.
That being said, when you're talking about 20+ year old used (muscle) cars, anything goes. Every car has it's own story so you'll find everything from rusted & ragged out pigs to low mile gems and everything in between.
When embarking on a longer journey, it helps to be knowledgeable about the cars and what makes them tick. Putting a few hand tools, a scan tool (with a list of error codes) and possibly a couple spare electronic parts in the trunk can be a good idea.
Also, before you do anything after you buy one, put one or more anti-theft devices on it. About the worst problem you could have on a trip is losing the car.