Sorry, but scanned copies of the FFL are NOT acceptable, only faxed copies, as stupid as that is.
There is also a bit more work to transfering a firearm than people want to admit and problems can occur. First, a signed copy of the FFL must be sent (or now a faxed copy), which means either a stamp or a long distance phone call. The FFL should also check to make sure that the person has a valid FFL (know who they are dealing with) or make sure they get a copy of the person's driver's license. Someone has to be there to accept the firearm when it is shipped and sign for it, assuming it is correctly shipped, which often is not the case. Then it needs to be logged in the bound book. You need to call the person who order it to let them know that it has arrived. Once the firearm arrives, the person will inspect it, but what if there is a problem with it? What then? If the firearm is shipped back, the FFL needs a signed copy of a FFL, which is a problem if a private party ships it. If the firearm is acceptable, then the paperwork needs to be filled out. Once the transaction is done, the bound book must be updated. All of this takes time, but people don't see or understand that.
Problems are really a problem. Who pays for all the time and effort which results? For example, in one case the receiving FFL had no mailbox and failed to mention it. Since shipping is required to premises address, this can present a problem if you want to ship a handgun for a reasonable price (USPS is around $15, depending on the value and other means are over $35). So, the firearm is mailed (also have to fill out form 1508, which some FFLs don't realize) and then no delivery is attempted and it is returned. Got to update the bound book. The USPS does not want to return the money, but did not attempt delivery, so spend time fighting to get the money back as the buyer and seller don't want to pay the money. Spend time finding another FFL and getting a signed copy of the FFL and start all over again. Instead consider getting a firearm from a known location, which do you think is easier?
The FFL can get stuck in the middle with no one wanting to pay, so why would a FFL want to get in that situation? When a FFL is willing to do it, the people often don't appreciate the cost since there are lots of license fees, then when the FFL is required by law to collect sales tax, they are accused of trying to rip people off and the people never try to find out what the law really is.