Of course, there are always exceptions, but I stand by the criteria that I suggested..... mainly years of experience coupled with a considerable knowledge of fresh water biology.
I seriously doubt that this 30' x 40' pond will be a dedicated Koi pond, but it is a remote possibility. More than likely this will be either an eco-system pond or a fishery pond. In the latter case it may be lined or earthen bottom or both. Whatever the type it must be designed and installed to accommodate the species of fish and/or other wildlife it may support. The typical pond installer would be severely tested by a project of this size, even many that are "certified".
"Everybody is ignorant, only on different subjects." - Will Rogers