In most states, you can get a VIN for licensing and titling purposes just by asking and having the trailer inspected for a couple of items by a member of law enforcement. They will look to see if it has proper lights and to be sure you aren't lying about it not having a VIN (i.e trying to get a license for a stolen trailer). This is pretty common since many people build their own trailers. As for having problems, since you don't know the specifications of the components, you are kind of at the mercy of how they built the thing. If they used wheel barrow axles and a hitch designed for a bicycle trailer, the thing could fall apart on you. Then your only legal problems will be with your liability for injuries it would cause to others. If the thing is well built, legal issues should ever arise. Just be sure you get a clear title showing the VIN (if your state titles trailers).
