Theres only one option that I know of. Azarius on Kerkstraat (up the road from Dolphins) has most of the same units in stock as their online shop (azarius.net). They also have a testing room at the back where you can try some of the more popular units.
"The Headshop" (near Basjoe) also has a better range than most places, but nowhere near the variety of Azarius.
Some vaporizers can be cleaned up like new, with others it can be tricky to remove all the resin. I suggest bringing some 99% isopropyl alcohol with you for cleaning, as its difficult to find in Amsterdam. Depending on what vaporizer you get, I also suggest disassembling the unit as much as you can, and putting the pieces in different places in your luggage (eg you can put a few pieces in with your camera accessories, some with your toiletries or whatever, use some ingenuity). This makes it less obvious in case they inspect your luggage. If all the pieces are together, its quite easy to work out that its "paraphernalia", in which case they might decide to totally search your luggage inside and out, do a swab test, or pull you into the side room for questioning.
No matter how well you clean it, theres always a chance they'll swab it and it'll still test positive for THC!
When I travelled with my used Flashvape, I threw out all the used screens before flying (they are replaceable) to minimise the risk. While its possible to soak them in ISO, and then boil them off, and in theory they should be totally sterilised and clean - They still have discolouration, and plus little stainless steel screens are generally only used for one purpose
Having said all that, the best option would be not to use the vaporizer until you get home, because you can never completely eliminate the risk of flying with a device that has been used. If its brand new, you can say its an aromatherapy device for lavender, lemongrass, chamomile etc, just in case the worst happens and they decide to question you.
Quite a few coffeeshops have vaporizers, so you can get by using the shop units while you're there...
