A number of years ago, I purchased a used Chevy Tahoe 4x4 which came with a national brand 2" receiver hitch (installed) as well as an electric brake controller installed. I did not buy the rig from a private seller, I bought it from a sales lot. The assumption is that you're ready to tow to the ratings of your vehicle and equipment.
A period of time went by, I was out camping, having some coffee, enjoying the view and looking over my Tahoe. The thought came to me that at some point in time I MAY opt to actually tow with this rig, and/or perform an off-road task involving use of the hitch. So, I set my coffee down and stuck my nose beneath the back of my Tahoe. What I found scared the bejezus out of me. There are four mounting points to mount this hitch to the rig, using four bolts/locking nuts. Upon inspecting it, this is what I found: 1. One tight nut/bolt. 2. One LOOSE nut/bolt. 3. One bolt with no nut. 4. One nut/bolt missing.
On my way home from camping, I stopped at a hitch fabrication shop in my area and explained to them my discovery and asked them if they'd throw my rig up on the lift and rectify the matter for me. Half an hour later I was on my way. The good folks charged me for the missing hardware (nuts/bolt) and didn't even charge me for the labor involved. Guess where I'm headed to if I need something fabbed up in the future.
The point is that one could assume this rig has been used by the previous owner to tow an RV with, or a utility trailer with since it was equipped to do so. Verify that what you see is what you SHOULD see by simply laying on the ground and looking. At BEST, this was 50% since it had three bolts and two nuts, and one nut wasn't even finger tight. I now know that it has all four and that they've torqued to spec, and ready to be put into service.