Very helpful info. Thanks. I do not have a trailer now but was aware of some of those inspections. I found some good options at some trailer super store in PA. Looks like around $6500 for a good one. A good chunk of change but I can get a lot more use out of it than just trash runs. I do a lot of built ins and a trailer can help make one delivery trip out of a bigger job.I do not have a dump trailer, so I cannot answer that part of your question. But as far as the requirements in MA, the only ones I'm aware of are the same for any trailer over 3k gvwr (which your dump will be).
You'll need an inspection sticker every year. There is a list of stations that do them on the MassDot website, but I'd call ahead because some of them list that they do trailers but do not.
If you buy new you'll have no trouble, but they check obvious things like lights, electric brakes, safety chains, and that the breakaway for the electric brakes is functioning.
You will also need chock blocks and cones or triangles (but they may not actually check for those).
I think that's all you need. You may already know all of this if you have another trailer.
Most of the info can be found here I think: