ATF considers that an activity proper to a Gunsmith. You need at least an 01FFL to make money doing it. If there is no profit motive, clean away. Also "occasional" jobs are exempted from the license requirement, so doing a couple a month for friends is probably OK. Also, if the owner is standing there when ya do it, most agents interpret that as exempting you also as you are not retaining custody of the gun overnight, something that requires records be kept by an FFL.If you had a business and all you did was professional gun cleaning, is that considered gunsmithing?
If it is a sale then you don't need an FFL.... but even that can go into a gray area as the BATFE never defines how many you can sell before they can say you are making a business of selling firearms. This is how some C&R's get in trouble. They buy up C&R's and then sell them at a profit. The BATFE says you can do this as long as you are not making it a business or making income and are doing it to further your collection. They don't give a limit like 5-10-25-50 per year etc.; not sure if they did this intentional or not.If it is FTF transfer, you don't need an FFL...right?
I do agree, there are some serious gray areas there.