I would ask a bunch of questions.
Are video games your favorite type of entertainment?
Do you play almost every day?
Do you prefer to spend most of your disposable income on games?
Have you played your whole life?
Do you enjoy most genres of games?
Do you follow video game news sites or magazines often?
Do you know at least some of the history of video games?
Do you watch television shows about video games?
Do you daydream about video games?
Do you discuss video games online?
Are you constantly planning the next games you will play?
Do you own multiple systems at the same time?
Do you play retro games?
Do you beat a majority of the games you play that you like enough to beat?
Do you challenge any games on their hardest difficulty level?
Have you ever purchased a video game soundtrack?
Have you ever read a book based on a video game?
Do you have any clothing or accessories with video game characters on them?
Eh, I'm sure there's more but I'm tapped for the moment. I would think there are different levels of hardcore as well. I answered yes to every question except "Have you ever read a book based on a video game?"
That said I fully recognize that there are people who would be considered much more hard core. I wouldn't be able to do an actual list of games I've beaten or played a lot because I lost count back in the NES days. Although I wish I had documented that through the years.
edit: I meant novel not strategy guide, but that might be a question as well.
