I've just today received a pair of used K702's.
Very happy with them, I must say (bass-light, I am not finding them, surprisingly, compared to the reviews on here: maybe a bit high-happy, but not bass-shy).
However, they are used. They were cheap (ish), and appear to be in very, very good condition, except the "elastic" in the self-adjusting headband is obviously stretched as it's doing; well, basically, feck-all. I'm finding them slipping down my head a little and obviously want to remedy this.
There are apparently ways to do so - a quick Google search has pointed me to many comments that it's possible, but no specifics. Trust me, if I could find it, I wouldn't be asking!
Any help, comments, or points to an appropriate post would be much appreciated!