Another used bicycle store in Leiden has opened!
It's called Guus, Second Bike and they've got a twitter feed.
They have a teeny-tiny selection of city bicycles for sale but it's a nice little storefront, conveniently placed next to a chocolate shop so that the disappointment of not finding a bicycle to purchase can be quickly remedied. And going back again and again isn't the worst thing in the world. :)
I've added them to the map!
View Bicycle Stores (used and new) - Leiden, Netherlands in a larger map