1 word.
Colbotron.
Colbotron is the part robot, part wizard, part supercomputer imp employed by G-mart.
I once witnessed him throw a nerd through a bookshelf for stating that Warren Ellis needed a haircut. Without a word, Colbotron then set the nerd on fire--with his mind.
Not wholly unlike Cerberus, Colbotron is pacified by music, in this case--Goldfrapp. If you ever enter the store when Goldfrapp is NOT playing, calmly back away, and do not, I repeat DO NOT look the Colbotron in the eye. Fortunately, no one has ever entered G-Mart when Goldfrapp is not playing.
Alright, seriously though, Colby makes the store. Apart from being abnormally affable, he makes great recommendations and knows just about everything about the comic/graphic novel universe.
price and selection are very reasonable, and if they don't have it, I'll bet you they can get it.