RetroGames has been 'gone' for the better part of ten years, but they were THE place to send Turbo systems for repair back in the day. And yes, they did have the official endorsement of TZD. It sounds like you had the misfortune of sending your system to them at the precise moment they disappeared. They were not scammers. I'm pretty sure I remember them disappearing around 2001, maybe 2002 at the very latest. They almost certainly were long gone by 2003. I say this because I remember where I was living the single time I tried to contact them (they never responded to my inquiry), and I'd moved out of that place by the end of 2002.
I've always wondered if they guy running the operation died or something based on the nature of their exit from the business.