While I agree that people should do their homework any worthy supplier can show previous successes, contracts I can not see as a valid option.
I think you will find every supplier will not enter any such contract. It is presumptuous to suggest they would. There are suppliers that will require a large percentage of the turnover to secure their professional support. Many people do not want to pay for those expertise so will not enter into a contract.
Suppliers generally support their designs however unless the operator employs professionals in aquaculture/plant culture or has the required skill themselves, there is absolutely no guarantee of success. Those skills can only increase the chances of success, not guarantee it.
If Joe Blogs wants to build an aquafarm, there is nothing stopping him but it is him that is ultimately responsible for the success or failure not the supplier. Imagine if one of the employees or himself do not notice a dead fish stuck in the outlet of a tank and it in turn reduces the flow rate and starts to kill the rest of the fish, even though the first cause for the death was a parasite. I can not see any supplier, saying “oh bad luck, please let me remunerate you for your losses”.
I have seen aquaculture farms go broke from the simple introduction of a deadly fungus in their hatchery. There are far too many anomalies for a contract to stand up.
There simply are no guarantees in this type of environment.