Sounds like to me he took in crap in trade for good useful parts. You got a housing and gears. What parts were these? Sounds like he did you a favor. He could have turned you away for inaccurate parts descriptions. 15x8 8 lug wheels are worth way more than a grinder that may or may not work.
Dollar for dollar I wouldnt have done the trade with you.
When I grow up I want to be like fourwheelerjeff