I am doing a flea market (inside) this Saturday. For anyone in the area, it is in the Schwelmer str. 10 in Flingern (Düsseldorf) from 09:00 - 17:00. The flea market is taking place in a disused machine hall so it'll be good even if it rains.
We've got everything you need (and plenty you don't but might like), funky secondhand clothes for grown ups and kids, antiques, preloved books, English and German, new things, crockery, pictures, some electrical appliances, telephones, new toys, oh you name it.... and some jam. It is all in a good cause. I am going to save my takings to go visit friends in China (silly people that moved away!).
Oh do come along. You might find the steal of your day!