When you're selling an RV, you are taking a big risk personally and financially.
There are so many aspects to take into account when selling an RV. Like selling a car or home, having it inspected by a certified professional will give a peace of mind to your buyer as to whether or not you are selling a quality product. A mechanic will look at a vehicle to examine it's roadworthiness. A home inspector will look at the livability of a home.
With an RV, you're selling a home on wheels: you need someone who is able to go point-by-point over the aspects of both. An RV inspector will give you an unbiased, professional examination and review, which can highlight issues the RV you're selling may have now, or in the future.