Hi and welcome to the forums! Keep reading on these forums, asking questions too, and do a "search" on Youtube.com for videos and demonstrations of virtually any subject you can imagine. On YouTube, just search "black tank RV" and you'll probably get a zillion videos to watch. (FYI, "black tank" is the tank that holds whatever goes down your toilet).
About the price ... I think it's too high. But, the value of any items is determined only by the price someone is willing to pay. So if YOU feel it is a good deal, then it is.
I do not think I would buy a used Weight Distribution hitch system. When I purchased my current one from my dealer, I offered to give them my old one to pass on to someone else. They said they could not resell or even give it away. When asked why, they said they could not be responsible for the loss of integrity of the system (time, wear and tear, bending, stress, and how structurally viable ot still is). I ended up keeping the hitch and chucked the bars.
I had my original Reese hitch and bars on 3 different campers over a 12 year period. The hitch head finally bent. OK now for a lightweight trailer, but not for a travel trailer that needed the bars. So I have the hitch, but never used it again.
I tried doing an internet search for your camper. I found some near misses, and prices are all over the charts, some much higher, some much lower than your friend.
Now ... can I give you a SOLID bit of advise? REAL WORLD experience here!???
If you want to keep this guy your friend ... DO NOT BUY THE CAMPER FROM HIM. Never, never, never do business with family for friends if you want to keep them family or friends.