Hi and welcome to iRV2.com. May I suggest asking more specific questions in the trailers forum? It is difficult to respond to very broad questions such as yours.
There are checklists available for taking delivery of an RV, but I think you are asking about the decision to buy rather than delivery time. One way to get a rig checked out is to hire a mobile RV repair service to check out the major components. They usually don't do chassis work, though, so you would have to get the dealer to tow it to a shop that does axles, brakes, etc.
Tires have date codes stamped on the sidewall. Make sure they aren't real old - probably less than 4 years for trailer tires.
2004 American Tradition; 2014 Buick LaCRosse
Homebase in the Ocala Nat'l Forest near Ocala, FL