If you let a striped keelback chew on you, how venomous are they? What would happen?

My striped keel back died within a month of me buying it from petco. No real way to tell who's fault it was, but I'm pretty certain it wasn't mine. The other day a guy at petco asked me if I needed help. Because I was looking at the striped keel backs they had labeled as garter snakes. I told him that they weren't garter snakes, and should be labeled separately(I'm 13). He got mad I think because I was younger and told me that I was wrong that they were garter snakes, their "suppliers" told petco so.