Google and Bing do NOT like ad filled and spam filled directories. They want local directories with quality businesses or communities listed, thus creating a real website with information that is relevant to that particular niche.
Same is said for a national directory that is specific to an industry. This creates natural links for the business and Google / Bing look very highly on this subject. They both believe that local should be the best search result and a nation dominant niche directory should be the best for that industry as well.
In any event, your SEO will help your website gain visitors and buyers. You cannot go wrong for the price to pay. A good directory like ours is the price of a couple of dinners, but dinners don’t last all year !