We get a lot of b&b bookings via natuurhuisje.nl - it's commission based and the only commission based site we use, but it does generate bookings. Mostly Dutch, but we have had Belgians too.
Regards
Anne
If there's no such thing as co-incidence, then why is there a word for it?
I'm not sure about B&B's but for self catering accommodation, I tend to get a lot of enquiries and bookings from immoweb.be. Just make sure you have your listing both in dutch and french though.