My wife and I looked at over 100 used rigs.... Not an exaggeration at all. We decided to pay cash for a used unit to see if we liked the camper lifestyle.
That unit served its purpose for three years and it taught me several things.
1) you will need to learn how to tighten screws... New or used, RV's are rolling earthquakes and screws, fittings, and moldings will need tightened up from time to time.
2) outside latches will break. It's just a fact of life. The sun will wear them out. Keep extras on hand.
3) tires on a trailer take a beating. Inspect them often, if you see damage or rot... Replace.... Learn how to read tire dot date codes. Your brand new trailer could have one or two year old tires. (Something I will not accept)
4) vent lids break, get caught in a hail storm, rogue tree branch, or even a mis step on your roof. Suggestion.... Install MaxxAir covers over your vents.
5) learn to do some inspection, try to not let your trailer go months without checking it out. Assume it will leak, because it eventually will. You must be vigilant and be aware that leaks can be external or internal and take care of them immediately
6) A $5.00 part can really put a hurt on your vacation. Learn the art of redundancy.
7) expect and accept that you will lose money....we don't rv because it makes financial sense. We rv because of.... Well.....insert your answer here .
8) remember if you buy new you are buying build quality and your dealer... Both are equally important. If you buy used... Your buying the previous owners TLC for the unit. If there was no TLC it's a bad deal.
9) for used if your nose smells rot.... No matter how beautiful.... Walk away. New or used. If the trailer doesn't seem right... Walk
10) the "perfect" trailer in a brochure or at the dealership may not be the perfect trailer in campground with you and your family in it. Be prepared for this.
I think that's all I can think of right now.
Jeremiah