Probably like most trailers, we set ours up in the front yard as if we were going to camp in it, setup the awning, fill the water tank, check taps.
You soon notice things that need replacing.
When it was all packed up i hooked it up to the car and pulled it up on some car ramps and spend a good bit of time inspectin underneath for defects and the like.
don't take the sellers word for it, take the hubs apart and replace bearing and check brake function.