I'll add my 2 cents here. Mark - I've seen stuff like you mentioned (swaying). The one time I was able to verify they didn't load the trailer correctly - incorrect tongue weight.
I've pulled a bunch of different trailers. All of them I make sure are loaded correctly. I've never had a problem - even in wind (slow down in the wind).
Since this sounds like a "bumper pull" trailer just remember the basics.
- don't overload the trailer! Just because it fits in the trailer doesn't mean it will be safe.
- make sure tongue weight is 10-15% of the trailer weight.
- make sure things can not slide around inside the trailer.
- get good tow mirrors so you can see around the sides of the trailer.
- make sure you have a GOOD brake controller installed (maxbrake comes to mind).
- all mechanical parts must be up to snuff (brakes, bearings, tires, etc).
- Don't exceed the hitch capacity.
For trailer weight - easy - go to truck scales (feed store, quarry, truck stop, etc).
tongue weight - I use one of these.
http://www.sherline.com/lm.htm If I remember right it was about $120. You can also use a bathroom scale and create a fulcrum and calculate tongue weight.
Hope this helps.
Dan