?

the person who buys my phone to restore everything?

I put an ad up on craigslist, selling an old phone that has been inactive for a long time. When i charged it to see if it's in good working order, everything was as I left it. A few days later, I sold the phone and noticed that as she left to enter her car, she was trying to get a button to work and I couldn't see anything happen on the screen. It's a relatively older phone. Perhaps it was lagging, or the many buttons she pressed made it freeze or simply do nothing because of her frantic button pressing? Now that I think back on the last few hours, I'm afraid that the phone has chosen this time to crap out on us and I'm scared of what she will do (in terms of rectification) if in fact the phone doesn't work. Anything I could tell her that might make the phone work? Could it be that is hasn;t been charged in a few years? She hasn;t called me back regarding this, but I'm paranoid that I accidentally sold a bad product. What do you think would happen? I would not have sold the phone if I knew for sure that it might have been bad. I'm always paranoid, so maybe this time I am again?