Welcome to the Forum! You asked a super broad question, which is hard to answer without writing a book. Fortunately for you, one of our esteemed forum members, Ed Felker, constructed an excellent crowd-sourced manual for the Vegas/Axis coaches. In it, you will find a lot of useful information and checklists:
BTW, as with used cars, some dealers detail and inspect coaches they take on trade. Some just put them on the lot as is. It is always buyer beware. Sales people might say anything to get you to buy from their inventory. A lot of buyers prefer to buy lightly used RVs, assuming that the initial problems are worked out. Your results will vary.