Backdooring is absolutely out of control these days. I got backdoored on two big items in the last 2 months, an SNES Fiber Optic and a NES Sealed Mike Tyson Punch Out. I do believe in karma and ethics (as I'd like to think most people do), but the price levels in the hobby have brought out the worst in people. Money is the root of all evil.
Having said that, I'm amazed that's the going rate on a controller in that condition. This is definitely my favorite N64 controller though and I made sure to seek out a Mint one many years ago. Congrats.