Don't deal with them. If they can and know how to post an ad ,they can use the pm system.
If deal goes south and you have time , place, location and all the details worked out in pm you can at least leave feedback to let others know their not trustworthy.
Then again it could be something you...
It's iPhone , mine does it too and has been doing it since about 2 updates ago.
Upload a picture/choose a file/photo library/ photo stream
Mine won't do it any other way