Criminal or Civil Case? selling on craigslist?

I sold a laptop through craigslist. I meet the person at starbucks where she checked it out for a half hour even calling her computer savvy friend to check out all the specs, finally she bought it. The next day she calls me for a refund because she said it wasnt as I described, it didnt have wifi(which I said it didnt) and it was older then I stated. I refuse to give her a refund. A week later I have an investigator(a real one at the police station) asking me questions. Says I could be committing fraud. Is this just a scare tactic? I do have 1 prior felony for larceny. The laptop wasnt stolen, it was acquired through an auction. I also used my alias name with her instead of my real name when meeting her, I don't know if that matters. Also I dont have a copy of the original ad, and I can provide a receipt for the laptop if needed.