I haven’t seen them personally, but there are some documented cases I found on the Net: A vending machine that promises the chance to win a PSP, but dispenses mostly underpants (presumably in mint condition).

But more to the point there is this case where someone actually made a second-hand report of a panty vending machine in 2002. Complete with a photo, but of course it is possible to doctor it:

According to the PhotoMann article, a used underpants costs 1000 – 3000 Yen if bought from this machine (6.10 – 18.30 Euro).

InventorSpot has some additional photos and points out that a vending machine that sells panties doesn’t mean that the panties are used.

However, my sources in Japan say that these vending machines really exist.