Just received a gun for a customer that he bought on the internet. Checked the sales sheet supplied by the seller and found the serial number they listed as being sent to me was different from the one listed on the receipt. Thankfully they listed their phone number and am having it corrected. So if you have multiples of the same item double and triple check to make sure the gun you are sending is the one you logged out to another FFL.
This is also important for the receiving FFL in that if the gun they said they sent to you is ever used in a crime the ATF will be wondering what is going on with your books!