I am not sure if I really understand what you mean by anonymous, but I believe GRAYPAY has a non disclosure agreement, that may fit your needs. www.graypay.com
I personally wouldn't buy from someone who was anonymous, I would find that a bit untrustworthy I'm afraid
What type of anonymity are you looking for? Do you want your information to remain anonymous or do you not want your business name to show up on your customer's purchase statement? Or it something completely different?
Unfortunately the byword for "anonymous" processors is caveat lector. The closest you'll come to a means to transact business anonymously is bitcoin. Just don't hold any assets in the digital currency, as the market is volatile. Conduct your business, and cash out, like you would at any casino table. Jon