My dad has a joke that every year during the summer, all of the crap in the US exchanges hands through the garage sales that dot suburbia. All your old junk goes out in the driveway, someone else will probably buy it and use it for a little while before it goes back out in another garage sale in the future. It's like the Circle of Life for tchotchkes and incomplete toy sets.
But at the same time, there's a little treasure hunter in all of us that wonders if we'll finally find the Holy Grail hiding within someone's box of old, beat up LP's. Since huge garages and yards aren't a thing in the Netherlands, the options for spreading the junk around are limited, so you need to take advantage when the opportunities present themselves. A few times a year, you can visit a rommelmarkt. The people "in the know" can find these things pretty easily (much like the garage sale hawks in the States), and as far as I can tell, they find them though a mixture of experience, pure cunning, and maybe some sort of animal sacrifice to the rommelmarkt gods - often the information on the internet is incomplete or nonexistant. But despite their elusiveness (to the foreigner) the sheer volume of resellable junk at a rommelmarkt is staggering and requires a bit of patience if you're hoping to find The One True And Complete Board Game or something really unique.
Fortunately, for those of us unable to divine when and where a market will present itself there is Marktplaats. Marktplaats is the Dutch Craig's List. It's open 24/7 and free to use - you just need to be able to read/write a bit of Dutch or use an online translator. The benefit of course, it that you can search for exactly the treasure you want or post an advertisement (providing you can figure out the right search terms) without having to fumble through your Dutch in front of a live person. But again, the amount of junk is staggering, but you can find some treasure, especially if you don't mind killing some time shuffling through the pages.
One thing to be aware of while searching through your local rommelmarkt or Marktplaats is that koopjes (good deals) bring out the crazies. IN DROVES. I've now bought and sold things at rommelmarkten and on Marktplaats, so I can indeed confirm that this is true. Through Marktplaats I had someone ask to pick something up at 5 o'clock in the morning (erm?) but luckily it's easy to brush someone off by email (especially when the address is hidden through the system). In person it gets a little dodgier, like when Little Man and I got stuck next to a crazy while selling at a rommelmarkt on Koningsdag. At first it was just annoying that she kept trying to get Little Man to buy the crappy toys she was selling. It got weird when she figured out we were American and wanted to rehash the events of 9/11. But I lost the ability to speak when I watched her buy up a bunch of tennis balls from another guy, then demand to return them with her money back when she realized he had more and would be "competition." Cue cuckoo clock sound.
But, if you can wade through the junk and keep your wits about you, these places can really give you treasure. At Tilburg's Meimarkt (a massive overnight rommelmarkt) Little Man found a sheep's jaw bone and Mark found some great LP's. And on Marktplaats, I found Little Man's bike and my amazing Pfaff 30 sewing machine with the hand crank.
Have you been to the rommelmarkt or used Marktplaats? Was it worth it?