Secondary sales of firearms, or sale by private sellers, refer to the transfer of firearms by persons who are not required to be licensed as firearms dealers under federal law. Federal law only requires persons to be licensed as dealers if they are "engaged in the business" of selling firearms. People, who do not sell firearms for a living, generally do not need to obtain a federal license.
Since private sellers are not federally licensed, they do not have to run background checks on prospective purchasers under the Brady Law. Private sellers also do not have to comply with other Brady Law provisions, such as keeping records of sales of firearms, or selling firearms from a specific business location.
However, private sellers still must not sell firearms or ammunition to anyone whom the seller knows or should reasonably know is under eighteen years old or is otherwise not allowed to buy firearms.
Many private sales take place at gun shows. As a result, the lack of a background check requirement for private sellers is often called the "gun show loophole" for prospective purchasers.
If you have concerns about the laws regulating the sale of firearms by private sellers, talk to a criminal law attorney with experience in firearm regulations. Firearms sales are governed by a complex array of local, state and federal laws, so get expert help with you firearms sale problem immediately.