Be sure you have a screening questionnaire if you are going to reduce rent for help with farm work. I do that with my farm house rental and it is amazing what kind of people apply for it. I have people who used to visit their grandfather's farm, went to horse camp before, or are sure they could learn really fast.
CL seems to work okay. Try your local BBs, particularly electronic ones. Word of mouth is good.
Be sure to check references and be clear about expectations for farm living. For example, we want our front gate kept closed and we don't have an automatic gate opener. So you have to get out of your car, open/close it. I've had to terminate the lease with a tenant over his inability to keep my gate closed. He just didn't see the need to shut the gate when he was leaving for the day, so my property was unoccupied with the gate wide open to the road. Not cool.
We advertised our basement apartment on horse property & we found super renters on craigslist. You have to screen a bit but it can payoff. Our renters' have been with us for almost 2yrs & I love having them around!! We just have them pay straight rent but if we go out of town or have projects around the farm we just agree on a price before hand. It seems to benefit both of us!