There's a used bike sale next weekend sponsored by Phoenix Bikes and a few other bike shops.
Saturday, December 12 from 10am-2pm at Big Bear Cafe (at R and 1st St NW DC)
can we bring our bikes to sell?
According to my friend, who volunteers with Phoenix bikes:
No, the venue is only set up to sell bikes that the kids and
volunteers from the local youth and co-op bike programs have been repaired and refurbished. It helps them do some fund-raising and advertising to the community.
WABA sometimes has bike swaps, which might be what you're thinking of: http://www.waba.org/events/bikeandgearswaps.php