I think that you also need to perform a few web searches using English key words. Then find out the commission rates of the companies who are highly visible to the english market. Also go on
Properties for sale, homes to rent, overseas property, retirement properties and new homes on rightmove.co.uk and review Marche houses in the overseas property section, these agents are also highly visible and shoud be considered. For all the sites ask what kind of traffic they receive a month and how many enquiries. I think that you would do well to do the same for the Dutch an German markets as they are more bouyant and haven't suffered currency devaluations