Can I get in trouble for this on Craigslist?

A lady contacted me for my ad that I wanted to trade my HTC Sensation for an iPhone.
We agreed (after we sent pictures back and forth to each other) that we wanted to trade.
Her phone had the screen cracked on the back and mine had normal wear and tear.
Now she is emailing me saying that the top right of the screen had went out, it worked fine when we traded.
She looked at the phone and had no problems with it, she took it and I took her iPhone 4 and that was that.

Am I obligated to give her the iPhone 4 back?
Can she call the police about this and me get in trouble?
I think she dropped the phone and now the screen isn't working & I don't want the phone back.

What do I do?

She can't call the police about it… Well, she could but I feel sure they'd just tell her something like 'tough luck'. You're probably right, she messed it up and wants to trade back. If she inspected it and accepted it, it's hers.

This is tough… You really have to see exactly what the problem is. Maybe she just doesn't know how to use it properly?

"Now she is emailing me saying that the top right of the screen had went out, it worked fine when we traded."

You gave no warranty, She has no case. It would be a civil matter. The police wouldn't get involved unless there was evidence of fraud. Tell her that the phone was in good shape when she got it, and you don't want it back.

"Let the buyer beware" is appropriate here.

Ignore any further contact with this woman. She's an idiot without a case.