Hey... I cannot say this doesn't happen to me... But I was lucky that every time I responded: "Really? This is not your card? O_O''?", they answer me: "No, that was my card. Nice trick"... Althought, when they answer me that, I realized they don't really care about the trick, because somehow, they don't really like magic... Or, at least, that's what they made me feel on those moments...
I read every response to this thread, and I think (at least, for me) that is impossible to predict someone gonna lie to you if it is the first time you gonna perform for that person... Of course, if you already had a little chat with him/her you can maybe predict his/her reaction, but it's too much to worry, I think...
What I would do on that situations, could be something like "How-to-save-a-trick-if-you-screw-it-already"... In my opinion, if you already started the performance, and revealed the selected card at the end of the effect and the spectator tells: "That's not my card...", I instantly would ask: "Really? Wasn't this?", and if he/she answers me "NO", I would ask for his/her "selected card", and at the same time turn the deck face up and cull or cut to the top the card he/she named. Later, make a color change with the real selection and handle him/her that card he/she just named... Could be a color change, a top change, a card-to-pocket or card-behind-the-ear or card-to-box or anything new, but with the card he/she just named... That way, you just not only shut his/her mouth up, but also performed a second "impossible" effect...
I think now-on, even when someone tell me: "That's not my card... Nah, just kidding", I gonna (at least try to) cull the other 3 of the kind to the top or bottom of the deck and make them appear somehow, backing up on the excuse that "he/she maybe confuses the selection with one of the other 3..."
Hope something of all these can help you... And good luck with your teenage audience LOL