Magical Powers Manifesting in my Flat

Got a visit today from the Immobilien office that is going to sell my flat. I wanted to make them a fair offer, but they just laughed at it. The man pretended like I was some stupid blond naive floozy, that doesn't know her way around things ... We 'll see about that, won't we ?
I showed the man around my flat.
'Oh, I remember this flat quite well', he baffled, 'from the time, three years ago, when we rented it to you'.
He walked around like he remembered, but I think his memory failed him on the big cellar that I hid from him by means of boxes and dirty clothing ... He doesn't have a clue what he is selling ...
Then he walked in my garden, stamping on my plants, as to 'measure' it.
'So my man', I asked crispy, 'How big is it then, my garden?'.
It appears to be 65m², measured by leisure suit man's footsteps.
I also have a bit of a 'wall' problem, as you can see on the picture. This wall is situated in the middle of the flat, between the corridor and the bathroom.
'Seems to me, that there is a pipe from the central heating broken, or maybe a pipe line from the water providing system', I said keenly
Shouldn't have said that, I really shouldn't. This is what truly, honestly happened ...

And Whoo, The Man from the Immo, He laid both His magical hands upon the wall, touching it and caressing it. Then He spoke the following Wise words to me: 'Woman, that wall is as dry as a cookie! Just a little bit of painting, and it will be alright again! This, this is merely ascending moist, you have that in a newly build building' (in anno 2000 ...)

'So you don't think it's a pipeline that is broken ?', I replied surprised and astonished by so much wisdom.
'Woman', he answered, 'You are totally wrong, there are no pipelines in that wall (situated between the water boiler and the bathroom), it's just an easily fixed problem'.
I was blown away by so much wisdom. I didn't know there were such people that could tell the value of a house, just by stepping on plants and putting their hands on crumbling walls! The world is such a magical place !

So I made them an offer to buy my own flat, I will know by the end of the week if they accept it or not. It's out of my hands now. But, as a reminder to all future buyers that 'll come to have a peek inside my flat, I put up the following sign on the scruffy wall :

It's an old pamphlet from previous elections, warning us against extreme right dangers. The sign says in dutch:

DON'T BUY A BLACK CAT IN A BROWN BAG ! ! !