Under the GCA, selling of firearms to certain categories of individuals is prohibited.
(d) It shall be unlawful for any person to sell or otherwise dispose of any firearm or ammunition to any person knowing or having reasonable cause to believe that such person - (1) is under indictment for, or has been convicted in any court of, a crime punishable by imprisonment for a term exceeding one year (2) is a fugitive from justice; (3) is an unlawful user of or addicted to any controlled substance (as defined in section 102 of the Controlled Substances Act (21 U.S.C. 802)); (4) has been adjudicated as a mental defective or has been committed to any mental institution; (5) who, being an alien - (A) is illegally or unlawfully in the United States; or (B) except as provided in subsection (y)(2), has been admitted to the United States under a nonimmigrant visa (as that term is defined in section 101(a)(26) of the Immigration and Nationality Act (8 U.S.C. 1101(a)(26))); (6) who (!2) has been discharged from the Armed Forces under dishonorable conditions; (7) who, having been a citizen of the United States, has renounced his citizenship; (8) is subject to a court order that restrains such person from harassing, stalking, or threatening an intimate partner of such person or child of such intimate partner or person, or engaging in other conduct that would place an intimate partner in reasonable fear of bodily injury to the partner or child, except that this paragraph shall only apply to a court order that - (A) was issued after a hearing of which such person received actual notice, and at which such person had the opportunity to participate; and (B)(i) includes a finding that such person represents a credible threat to the physical safety of such intimate partner or child; or (ii) by its terms explicitly prohibits the use, attempted use, or threatened use of physical force against such intimate partner or child that would reasonably be expected to cause bodily injury; or (9) has been convicted in any court of a misdemeanor crime of domestic violence.
Exceptions as quoted from DEFINITIONS GCA Sec.921 section B
(ii) A person shall not be considered to have been convicted of such an offense for purposes of this chapter if the conviction has been expunged or set aside, or is an offense for which the person has been pardoned or has had civil rights restored (if the law of the applicable jurisdiction provides for the loss of civil rights under such an offense) unless the pardon, expungement, or restoration of civil rights expressly provides that the person may not ship, transport, possess, or receive firearms.