Credibility issues with a legitimate company

Recently i received a phone call from a potential client, and he told me that he is reluctant to work with our company. His argument was not very clear but he let me to believe that "someone from the same branch" instructed him that we might be a scam. The reason for me joining this forum was to check up on possible scams and frauds and to confirm suspicions i had about different emails and companies. Unfortunately as the wheel has turned, i must now find a way to counter future "benevolent" real or fake competitors.
Although i tried to reason with the client, and gave him the registration number for the company, along with the Chamber of Commerce website where to check us out, i am more than sure he did not bother to do so.
I am, at this point, opened to any suggestions, and any advice will be more than appreciated.
Also, for the native American/British English speakers, i do apologize for any spelling mistakes i might have made, as i wrote this email in a hurry and tried to be as explicit as possible.

Thanks in advance.