Hey there!
I work in The Hague, independently without registering although it's not the wisest thing to do. Please don't ban me on this post as I am just sharing my thoughts. I would love to register myself (and do all things legal e.g pay tax etc) but despite legally able to live and study here, I am not allowed to legally work. If you can register, by all means please do, the system helps all parties.
Let me throw in some comments/tips/etc on working in Netherlands in general.
Working in NL
1. The window girls really have it hard especially in the RLD as the window rent is around EUR150 per shift (not even 24 hours). This is an info I got from Punters so I'm not sure how 100% accurate is the information. Sometimes the guys in the RLD don't even take up the service and only turn up for entertainment, which is really sad.
2. Amsterdam would not be the best city to work from as there is an influx of girls from all over the continent, but again, if you can market yourself well, why not? The big cities like DH, Utrecht and Rotterdam would be a better bet. Maybe if you work in a nice neighborhood in Amsterdam that will play in your favor? However, Amsterdam rents are expensive. Another tip I heard is to work in Zuidas where the financial district is, so you get lunch crowd clients or after work clients. Zuidas is equivalent to the City in London, though on a smaller scale.
3. There is a quota for the registration of sex workers in every city and it's a department in the City Council that issues the 'license'. Most cities have reduced the quota year by year making it hard to obtain this. It's always safer to work a card but I know alot of girls work independently.
Tips
1. The most traffic is from Kinky.nl. You can advertise as an independent in Kinky without any "license" or "registration number" but you will need to go through the verification process as well such as holding your ID card with the latest newspaper etc. They want to make sure that you are above the legal age and that you are permitted to be in the country. The process is fairly easy and quick. The Kinky admin are pretty nice people. You can pay EUR2.00 via credit deduction from your phone so your ad is in front or something like that. I think EUR25.00 for always to be on top. When I advertise, I usually pay the EUR2.00 so my ad stands out
2. Another website to advertise is sexmarkt.nl and sexjobs.nl though from my experience, there's not much traffic coming from here. All of the websites are in Dutch but easily translated via google translate click.
3. I'm quite wary of working independent so I only work after office hours or on weekends, and I have uni too so that keeps me busy during the day time. If you're attracting too much crowd or traffic (but working without a license), you might get a visit from the authorities. The authorities will consists of polices (a man and a woman), tax officer and a social worker. They will question etc and they will let you off with a warning for the first time but I think, they will issue a ticket or fine if you are caught again.
4. There's a free sex clinic in most cities that you can get checked anonymously and also for advise. I go here every 2-3 weeks. Depending on the frequency of my work.
5. There are alot of pretty girls on Kinky so make your ad stand out. Get a Dutch photographer who is familiar with the local market to do the photo shoot as she/he knows what/how/suggestions for your photos to cater the demands/stand out. I know a few and PM me if you need info.
Pretty much, I like my Dutch clients especially when I compare it to elsewhere. The ration of TWs is low. The Dutch clients are pretty polite, let you know if they are late or need to cancel etc. Most of them come earlier than the set time and some do overstay their welcome but it's usually just to chit chat. Most of them know the M.O and rules of the game.
If there are any questions, just gimme a shout. I might not be able to reply asap but I will try my best. Have a great week. Cheers xoxo