When not in person to make the transaction of a non-restricted firearm. The seller asks the buyer for the information on the PAL card(Name as it appears on the card, PAL #, and the expiry date), then calls the CFP at 1-800-731-4000 to ask if the PAL is still valid. If the person at the CFP says yes, then that is all you need.
For a restricted or prohibited firearm transaction, the seller does not need to verify the PAL, the CFP will do that themselves during the transfer of registration process. The seller just needs first ask for the PAL number and name, then to call the CFP at 1-800-731-4000 in order to begin the transfer, then gives the reference # provided by the CFP to the buyer to then call in and initiate the transfer from the buyer's end.