Anyone have some good info about Nothing in Life is Free dog training?

This weekend I am puppy sitting a 6 month old lab/GSD mix (male, scheduled to be neutered next month). He's sweet, and pretty good. With a major exception. He is very possessive/food aggressive. You cannot take anything from him without him growling at you (that's something I've never allowed from any of my dogs; they all learn from the time they are babies that I can take anything out of their mouth). I don't know what his background is, other than he came through a GSD rescue.

Tomorrow, when my friend picks the puppy up, I want to be able to give him some ideas about how to stop this behavior. Any suggestions?