One of the most commonly-asked questions, at the shop, when I was selling a trailer was, "What is the weight limit?"
"Well," I would tell them, "the manufacturer recommends 100 pounds, max..."
What I didn't tell them was that the trailer would carry many hundreds of pounds, if they wanted to pile it in. The problem, then, became a lack of stopping power, on the bike. The tires on bikes just don't have enough rubber on the road to safely stop a heavy load.
I know all of this, because I once pulled a Burley trailer, loaded with all of the supplies for a shop picnic (grill, charcoal, beer, food, ice, etc., for 15 people). I think the trailer probably had 250 or 300 pounds in it, plus the 160 pounds of me on the bike. Add in the 25 pound bike and 20 pound trailer, and I was rolling a GVW of 450 to 500 pounds...on 1,9" mountain bike tires...on a gravel road.
I didn't want to tell people that the trailer would handle more weight than recommended, because I was afraid they might be as stupid as me, and overload the thing! I didn't want to be responsible for someone getting hurt.