I have had that happen to me before a couple times.
When I knew about this up front (I asked who was doing the paperwork) I ended up not buying anything from that particular dealer for the sole reason that he wanted to do the paperwork and I didn't want him to. I didn't argue about it, I just bought from somebody else.
The dealer I now buy from is perfectly happy with me typing up the paperwork. He is interested in doing business and doesn't need his ego massaged by assuming a position of power by insisting on chickenshit stuff like you describe. I have done 19 transactions for NFA weapons from this guy so the money offsets his disappointment in not getting the thrill of lording over me.
Many (most ?) dealers gets a feeling of power from this kind of bullshit. They spend their life being bullied by their wife and have been wimps their whole life so when they get an FFL, they think this makes them somebody. This is their 15 minutes of fame. The power trip these losers are on is incredible.
I just bought a couple suppressors from a dealer that I had never dealt with before, and I didn't ask about the paperwork. They pulled similar bullshit on me. Delayed my getting the paperwork by about a week. The paperwork takes about five minutes, but because they want that feeling of being in charge they delay the process by a week. Instead of immediately typing up the paperwork and handing me a copy, the dealer had to have a secretary in another location do it, then have me drive all the way back there to pick up the completed paperwork.
After I got the paperwork from them I realized that the FFL holder hadn't signed the form: he is out of the country. So, they want me to get the CLEO signature then return the paperwork to them for the FFL holders signature which no doubt will delay the whole process at least another week. If the FFL holder wasn't there to sign the paperwork, I could have done the paperwork at home (without his signature) and got it submitted for the CLEO signature a week earlier.
I also realized that they had screwed up in typing their FFL number and instead of just doing the form over again (take another five minutes) they just wrote the correct number over top of the incorrect number with a pen.
This is the kind of bullshit I try to avoid by doing the paperwork myself. That form is not only going to have to pass muster with the ATF, but I am going to have that form probably for the rest of my life. I want to take the time to do it right and not cross shit out or make corrections in pen.
This is a tactic that has been used by dealers on two of my forms including the first one I ever got: they made a mistake and just crossed it out with a pen.
So, since it wasn't signed, I just took the five minutes to do the form again so it is printed out with the correct number and nothing written in pen. Not only is it the neat and professional way to do things, it removes any doubt that you altered the form after the fact.