Hi,
The read more tag is fine with #description.
The issue is that your template is setting a base tag in the header of the page which is:
<base href="http://www.sanitair-installatie.be/index.php/component/hikashop/product/55-1-greeps-mengkraan-keuken-f100-chroom">
But the URL of the page is
www.sanitair-installatie.be/index.php/co...00-chroom?Itemid=200
The easiest is to simply remove the base tag from the template as it should not be needed and it won't cause that issue.
Alternatively, I think that you should unselect the menu that you selected in your products listing modules via the menu Display->Content modules (all of them, especially the unpublished ones). That way it should pick the current menu for the itemid and it should remove the issue of having your products displayed by a non existing menu.