I do a lot of utility riding, and use 2 wheel Kid's trailers a lot (plus a custom trailer for the big stuff).

For the kid's trailers, they do best with < 100 lbs, although, some of the vintage ones with a full wrap around frame and quick release wheels can go a bit heavier.

I have, on occasion, taken a trailer out on road trips (150 miles or so in a day), usually < 50 lbs, but I prefer to keep as much loaded on my bike as possible without a trailer.