We looked at used trailers and I know if I was selling a used trailer privately, I would be very leery of someone taking it for test drive. We knew what we wanted so we bought a Sherline tongue weight scale to check the TW of the trailers we looked at. The door stickers and such did not mean as much to me as the TW. We did very well in our decisions and avoided a bunch of trailers that we liked but were too heavy on the tongue. You can check the sticker on the trailer for max weight and dry tongue weight and then weight tongue. You will have an idea of what your loaded weight will be looking at where the tanks are, storage is and what is on the tongue (propane, batteries, etc).
My rule is when you don't have much information, having the tongue weight is a benefit that tells you alot (thoughtful interpretation needed).