Quality of frozen rodents in different stores?

I am a big believer in you are what you eat. Especially when its something like a snake that only eats rodents. If the rodents aren't getting the proper and full amount of nutrients either are your snakes. So what is there to tell you store v.s store on the quality of feed you are giving your snake? Obviously if im breeding my own rodents i know what i feed them. Or a place like rodentpro.com i can definitely trust them. But what about places like petco or petsmart say i run out of my own feeders and need to get some quick, are those rodents fed the same quality of food?

There really isn't a way to tell other than by sight. Unless, when you thaw the rat and it already smells rotten or the snake keeps regurging. That's about all I can think of...