I buy almost everything from Amazon. They can definitely be trusted. It's true that you may be dealing with another supplement company through the Amazon Marketplace. I like that I can sign up and register with one company and not have to give my credit card out all over the web. I set up their 1 click setting and regularly buy supps on my phone.
A lot of times they might also have better prices. I've bought Trenazone, Forged, Andro Mass & Hard, HCGenerate, C4 Extreme, Alphamine, Formastane, just to name a few.
Much easier in my opinion.