Even buying "new" trains from dealers, who may appear reputable, involves risk, as I learned the hard way recently after purchasing a new old stock Legacy K4, out of manufacturers warranty, but nevertheless new in that it hadn't been run nor tested. It arrived with loose motor mount, screws rattling around in tender, and bad Railsounds Lite board.
The other item I learned is find out who is responsible for return shipping before you buy. The above dealer charged me a hefty initial shipping charge, and they're only in an adjacent state, yet wanted me to pay for return shipping for repairs. That's when I did my research and found out that while they're an authorized Lionel dealer, they're NOT an authorized repair center. Fortunately, I know Gunrunner John and took the item to him for repairs.
After this fiasco, I'd rather have items tested, but only if they're an authorized repair shop or someone I know of and trust who knows trains.
