Looking at online bike listings is a constant, and perhaps, bad habit of mine. I'm not trying to break it yet... (until I have the perfect bicycle... Once I have that, I'll stop. Yeah.)
But luckily in the Netherlands I've found just two sites, and only one has decent bike listings.
There is a craigslist / amsterdam and it covers the entire country. Most listings are from the Amsterdam area and they are usually English language. There are many listings of expat furniture, pleas for car rides to Germany and offers for babysitting.
... with occasional panicked bike listings by people who describe their bikes as 'lady bike' or 'bike,' without including photos.
This is what craigslist is like in the US. It's busy, full and in the native language. Marktplaats.nl.
Excellent practice for learning Dutch! And if you respond to a seller, broken Dutch is expected. Who uses proper sentences online anyhow?
The bike listings are immense, with photos, in multiple categories.
Fietsen en Brommers (Bikes and scooters)
Dames, Heren and Bakfietsen, Racefietsen, Toerfietsen, Omafietsen, Ligfietsen (recumbent), Tandemfietsen, Mountainbikes, Kinderfietsen, etc.
There's lots of other stuff for sale, too.