I've seen a lot of pros and cons on the Harbor Freight trailers, so I thought I would provide some feedback on my experience with one. I have a 4X8 folding trailer with 4.80X12 tires. I bought the trailer new about five years ago for about $250 (with coupon) and it has seen moderate use hauling construction materials for home projects, hauling my riding lawnmower, hauling construction debris and trash to the landfill, and moving my son to and from apartments near his school about 80 miles away. I have not overloaded it, but I have pushed its capacity of 1,100 lbs to the limit according to the landfill scales. I would estimate that I have put about 1,000 miles on the trailer in those five years and I have driven it mostly at highway speeds of 55 - 60 mph. I always check the torque on the lug nuts and the air pressure in the tires before each use. I have not done any maintenance on the trailer in those five years except to repair some wiring that was chewed up by squirrels and paint the faded (to pink) exposed sections of the tongue. I have never folded the trailer but simply keep it in the back yard covered with plastic and tarps. It has a 5/8" untreated/unpainted plywood bed that is worn from use but with no rot.
Today, I decided to re-pack the wheel bearings and just give the trailer a good inspection and cleaning all over for the first time ever. I found the bearings and races to be like new. Even the machine grooves in the axle were still visible under the bearings. (I did re-pack the bearings with new grease when I built the trailer originally.) All bolts were tight and there were just two very small spots of rust, one on a galvanized fender bracket and another on the heavy frame bracket that holds the two hinges and the axle spring supports. All the other paint and galvanizing were in excellent condition. All the lights still work fine even though the little clip fasteners are rusting badly. The only thing I found of concern was some minor cracking in the sidewalls of the tires and that was only on the outside walls. The inner sidewalls and tread are still like new. I keep the tarps down over the wheels while in storage, but they still get some daylight (and UV).
In my opinion, you can't beat these little trailers for the price, and they are safe and quality products if used within reason. That is why I am using the slightly heavier (and wider) Northern Tool version as the basis for my weekender build.