Factory dry weights should be quite accurate. Many are weighed on a scale.
It is the catalogue dry weights that can be very inaccurate as they will not include the options. And some manufacturers are definitely worse than others as some have all the options "included" and others do not. For example my Trailmanor Elkmont's catalogue dry weight did not include "options" that were actually required!
So I always check the yellow sticker on the lot to get the factory payload (GVWR minus Dry Weight).
One thing I noticed recently is that the double pane thermal window option always adds hundreds of pounds to a trailer's dry weight. So if you want this option, make sure the catalogue says you have a lot of payload.
The catalogue payload of our new trailer is 1850#, but its factory payload on the yellow sticker is only 1181#, primarily because of the thermal windows. Typically, when I asked the salesman over the phone what the payload of the trailer was he just quoted the 1850# number without even looking at the actual trailer.
