branno, as far as my knowledge and experience go, you should not be anyway responsible for "parts" --- in as parts for equipment. Normally you are "paying for a service" only.
Our caretakers also significantly 'sub-contract' . Especially for milling rice.
We would never consider paying for machinery, equipment,maintenance, or parts etc.
Concerning harvest yields, fertiliser and snail bait we just have to "accept" the ultimate cost as told to us. But I also know the approx cost anyway which should not be so expensive. Also with water to keep everything fresh and cool . Different fertilisers for different growing stages are added including granular and foliar sprays. These are quite expensive. I think our bill for fertilisers is gonna be somewhere around the
P5k-P7k. It does differ with each crop. We use hybrid seedlings and get 3 harvests per year.
Weeding is also done by hand if necessary. We usually pay the caretaker P250 each time he needs to do it.
We have a very good idea of all cycle costs and individual costs so we also have a good idea if we are being 'skimmed'. We know just how much yield we should get (approx) and we know how much cost (approx) so we also know how much profit (approx). Well so far no probs, but if ever we have some real concerns that we are being cheated we will just leave the field fallow or sell it.
Plenty of ricefields and plenty of caretakers.