Never heard of this happening before. I bought over $1000 worth of stuff when I rebuilt an N62 4.4 and they said I can return them for store credit since the engine is damaged and I am now rebuilding a 4.8

Maybe e-mail them or something, you may have just talked to someone who was having a bad day or misunderstood what you wanted. I always e-mail them and they have always been good to me about returns. It is not their policy to require such documentation from a "certified mechanic"...