You really need to check everything and I mean everything over. There will be no warranty so buying as is has its risks. May I recommend using this form?
Pre delivery checklist This is from the Keystone owners forum. It is a pdf file and safe to download.
I have used this list on the last 3 new fifth wheels I bought. It save me huge $ in inconvenience and time. It will also work for a used model. Read it thoroughly and follow it to a T. You won't regret it. You will then know exactly what you are buying and gain working knowledge of the rig at the same. Time. If the seller isn't willing to allow you to spend the time and do these things, then move on.
Goodluck.
