I know that whenever we've bought or sold cattle, the buyer backs up to a proper loading area, and the seller makes sure they get on the trailer. If this guy really wants to sell these cattle, I wouldn't give him a cent until he caught them himself. They are his cattle until he gets a cheque, so if he wants that cheque he needs to catch them himself. What if one got hurt while you were trying to catch it? Who is responsible? Would you still have to pay for it?
Just my opinion.
But if you decide you want to catch them, food works best, especially if the seller doesn't want them chased much. Take away their feed, and shut off the water. Come back in the morning, and they might be more cooperative. Cattle aren't like horses when it comes to coming for bait feed. They need to be hungry to really care about it.
I don't know of any animals that would load directly into a trailer in a pen that size except maybe our bulls. They know there are always cows at the other end of the ride, so they love the trailer. :wink: If the steers (and your helpers) will be quiet, you can try putting the trailer in the pen, parallel to the fence, near a corner, and walk them down the fence line to it trailer. Use the back door to funnel them in. It's an extreme long shot, and they need to be quiet, but sometimes it works.