Depends on the scale/age of your business/your ability to gain trust factors and reviews in other areas/your overall marketing spend/your industry. It is not what it claims to be, but a business with a BBB and no reviews is better than a business without a BBB and no reviews. But a business with lots of reviews is more legitimate than a business with a BBB. Also if the $500 is minimal to your overall marketing budget then do it. If that is less than your spend on adwords for the month then probably not worth it. If you are in an industry with a high scam rate then it means more. There are lots of factors and can really only be decided by you. For SEO it will get a backlink, it probably won't get leads, your local Chamber of Commerce is likely more valuable from a link perspective at the same cost (and can get leads and some local rep), though those are also hit and miss and depend on your industry.