marktplaats.nl

There are a lot of professional and amateur traders on Marktplaats. That's spoiling a big part of the fun. Just cheap advertisement from them or people buying more or less everything that is available and try to resell with as much as possible profit.
Business via Ebay in NL is almost zero. That's a sign.

I think it happens on all big sites like this once they reach a certain size. It's like on eBay here when you see people selling things at prices higher than on amazon. People assume they're getting a good deal but it's not always the case...