The old red-dog come-along, I still keep one in the tool box on my trailer, they will give you a work out.
When I was younger that is how you got a car on the trailer, the first winch I bought was a super luxury, they were expensive back then.
Easiest way if no winch is to jack knife your trailer, where your truck is pretty much out of the way, hook a long two strap to the old car and have the seller pull it up on your trailer with his pickup or tractor.
OK so this does not work for city stuff.