For me I read the bag and the ingredients on Royal Canine and all other foods. Not to hard to figure out the bad food verse the good ones. Than learn the actual companies that make them as well. Try to see where the stuff comes from. made In USA means nothing its where the ingredients are sourced from. That is the best way to learn these foods.
Most vets will say Royal or Science diet are good since those two companies make the no active ingredients prescription foods. The vets sell and profit from this.
IMO Royal is a scam and are marketing geniuses.