Take a look at the yellow tire load sticker by the drivers door. It will read total wt, including passengers, should not exceed xxxx. This is for your exact truck.
I would think that trailer would be a good match for your truck, with only 2 people, and an empty bed.
You can't trust sales person, but I think he means that a FW hitched trailer can handle more weight, than a receiver hitch is rated for.
You do need to count hitch and pin wt, as part of payload.
Let us know the door sticker payload,
Jerry