Gamedude is legit. I haven't been there in over a decade, but they have a long history.
I remember back in the day (early 90's) sending them my used games to sell, and a week or so later getting a check in the mail...
The store was pretty cool too, but I don't expect they have as much Atari Jaguar and Sega Saturn stuff as they used to!
Oh, and they are pretty easy to get to off the 405. However, depending on what day, and what time of day, "easy" is a relative term.