This one is hard to answer and would depend on a lot of things.
Have you actually met the seller, or has everything been handled through the internet so far? Does he have a "feel" for you?
How bad does he want to sell it?
How have your negotiations on the price gone?
When we bought ours from a private seller, we handled almost all of it through the internet. He was in Colorado and we were in Alaska and Mexico. He wasn't really sure he wanted to sell it. While he took a lot of pictures and time to answer our questions, he wasn't the type that wanted or liked to spend a lot of time on emails and counter offers trying to save pennies. We made him a reasonable offer below what he was asking and he accepted it. When we flew in to finish the buy based on actual inspection, he thanked me for the way we handled the pricing. He even filled up the 100 gal tank full of diesel, handled transferring over his warranty to us, put some food and water in the refer that he had running since he knew we'd be traveling right away in it and spent 4 - 5 hours showing us everything.
Some people don't let anyone in their MH and others invite everyone in. I'm not saying I wouldn't let you spend the night in mine if I was selling, but it would only be if I had a good feeling about you, I didn't think you were going to nit-pic everything to death and how much of a pain you had been during price negotiations. And, had I already removed all of my personal stuff from the MH. So, I'm not saying you're being unreasonable, but I can understand someone not wanting to do it.
Bill