Every August, during the heat of the summer, I drop my trailer off at the local trailer repair shop for both an inspection and maintenance.
So, my advice before buying, if possible, have the trailer inspected by an established trailer repair shop. Let them tell you what it needs and how much it'll cost.
Plan on having the trailer serviced yearly. Lights, brakes, wiring, tires, bearings etc.
I can do most of the work myself but don't. Having been involved in an accident, and sued, I want a receipt to document the service activities.
For we wrestle not against flesh and blood, but against principalities, against powers, against the rulers of the darkness of this world, against spiritual wickedness in high places.