Regulatory Notice 10-22 says that although Reg. D, "provides exemptions from the registration requirements of Section 5," of the Securities Act of 1933, these transactions are "not exempt from the antifraud provisions of the federal securities laws."
A broker/dealer (B/D) has a duty "to conduct a reasonable investigation of securities that it recommends, including those sold in a Regulation D offering." They must also meet suitability requirements, and SEC and FINRA supervisory and advertising rules.