I am confused. You say: “It's definitely a diamond” and “didn't look much like a diamond”. Whilst these phrases are not mutually exclusive, when you add: “he was pretty red”, it really does not sound like it was “definitely a diamond”.
The only positive way to determine the species is to post a clear, well focussed photograph of it. The pattern, let alone the colour, is diagnostically different in each. So those with experience would be able to tell you at a glance.
Whether you do it via APS or via a reliable experienced keeper, I strongly recommend you get someone who is competent to identify the species before you take any action with regards the seller.
With respect to the seller, on the basis of what you have told us, they are the sort of individual that is bad news for the hobby. Selling snakes far too young and then not being there to provide the back up that all respectable breeders do provide. If you think he has acted illegally, then definitely dob him in to the environment department. We don’t want these types.
I can only wonder if it is yet another example of a bargain hunter being prepared to buy a cheapie under suspect conditions. You can tell your friend that “2 weeks old” is suspect. Instead of being prepared to pay the extra dollars for quality animals and back up service. When will people learn, if you do your homework you will realise that basically you get what you pay for.
Blue