So he's swapping wood for your labor. You cut up( into rounds) as much of his downed wood as you want, leave it where it is, and keep half of the wood you cut? I guess it depends on what price you want to put on your labor, whether it's fair or not. As long as he doesn't expect any more than cutting and leaving rounds where they lay, it doesn't sound too bad to me. You want to be sure there is no question about how you will access ,load and haul away the wood. Establish all the ground rules and expectations first before you cut a stick. He might be a reasonable guy, or he might be fussy. A little more conversation may give you that answer. JMO