Looking for proof: Toxic to Safe

The store I work for has started selling Colloidal Silver ; from what I understand it is not the type that foams when shook which means it's one of the better versions. Still I find that I can't suggest this product to anyone as there are so many unanswered questions.

I have tried hunting through this and other forums, through medical journals (the ones I have access to) books, etc. What I'm looking for is how silver goes from being toxic to being safe.

I am looking for proof, as I cannot recommend something only to find out the hype was just like the hype of coke or heroin. I do, however, have an open mind and would really like for this product to be as good as some people have claimed.