How do I legally sell firearms?

To sell, trade or give an air gun that is less than 500fps, or a flintlock muzzle loading rifle, a PAL(Possession Acquisition License) is NOT required.
Laws can change from time to time. Here is the link for CFP so that you can verify that the above summary is accurate. http://www.rcmp-grc.gc.ca/cfp-pcaf/fs-fd/sell-vendre-eng.htm. Or you can call them at 1-800-731-4000.

To sell, trade or give a Non-Restricted firearm that requires a PAL(Possession Acquisition License), you must verify the buyer's PAL. You can do that by calling the CFP at 1-800-731-4000, or you can do it online by signing in here https://www.rcmp-grc.gc.ca/en/firearms/individual-web-services .  More specific information on how to validate someone's PAL is found in this article https://www.gunpost.ca/faq/how-can-i-validate-someones-pal .

Laws can change from time to time. Here are two different links for CFP on this topic so that you can verify that the above summary is accurate. https://www.rcmp-grc.gc.ca/en/firearms/buying-and-selling-transferring-… also http://www.rcmp-grc.gc.ca/cfp-pcaf/fs-fd/sell-vendre-eng.htm. Or you can call them at 1-800-731-4000.

To sell, trade, or give a Restricted firearm​, you must call the CFP to arrange transfer of registration, and to acquire an ATT so that you can legally move the firearm to your residence. You can reach the CFP at 1-800-731-4000
For more details and information, as well as to verify that this information is current since laws do change from time to time, please call the CFP at 1-800-731-4000. Or visit this link. http://www.rcmp-grc.gc.ca/cfp-pcaf/fs-fd/sell-vendre-eng.htm

To sell, trade or give a Prohibited firearm, you must contact the CFP by calling 1-800-731-4000. The other person will need the proper class of prohibited license to receive the transfer. The process for prohibited class transfer is similar to restricted class transfer.