IMHO, were I to build another pond, I would not go with the cheapest quote, but one with the most pond building experience and track record of success.
I do have a nice pond, but the higher quote would have been almost 2x price, but almost 2x size also. My smaller, cheaper pond dam was poorly compacted. The higher priced guy wanted to compact the snot out of things with a loader. If I knew then what I know now...

Of course I didn't join this site until after the pond was built, or my decision would have been different.