There was a time when I worked for a business magazine. My editor and I pulled an advertising campaign and refunded the money when a company appeared in the local press for fraud.
Having overtly bad advertisers is not good business. Keep an eye on the 'overtly' bad ones Mr Ajarn or they will destroy your goodwill. If your site gets a bad name there won't be any more advertisers.
Consider the advice it's from an experienced source.
FF.