None of my machines were "new" when I bought them. So, if it is a good dealer and they will give you some sort of guarantee I would say go for the lightly used one.

I have done this on the majority of my machines. I have only bought 2 new machine in my life. (That is a lot of years). My beloved Janome that is now close to 30 years old was a used machine when I bought it. The machine was close to $1000 new back in the day and I paid just over $500. the savings was enough to make it more than worth while. Right now is the first time I have ever had a problem with it and that is the curves on some quilting I have been doing. Heck, I have never even had her in for any service in all this time.
If your dealer is someone you trust he may even offer some warranty for a short time that will be the icing on the cake so to speak. I would definitely go for it! The dealer makes a bit and has a happy customer. and you have a new to you machine. Great for all involved including the machine going to a happy quilter.

I would not hesitate to buy used if there is a history on the machine, all original accessories are included (do double check against the new one), if there was a reasonable discount over new, and if the dealer is reputable. Given they mentioned a used one coming in, they sounds pretty up front to me, but as a direct customer, you can tell better.

Any warranty would have to be dealer-only (Janome, as with almost all brands, does not transfer warranties to second owners).

I bought a used Bernina years ago...off eBay!...and felt confident as we have a machine tech here in the Vancouver, BC area who does fabulous work. I knew he could get my machine up and purring. He's an independent (Eurotech) and I found him just by accident, but ask around the local quilt guilds to see if you have someone like that in your locale if you are thinking of buying used. When I finally saved up enough for a Featherweight, I took that one in too for a checkup and fine tuning.

I would let the tech go over the machine and do his/her tune up and then re-assure you that everything is perfect before you agree, although maybe put a hold on it pending that. Also, will there be a warranty?
I have a Janome 6500 and it is a workhorse. I wouldn't hesitate to suggest the brand to someone.
As to experiences buying used, I bought my mid arm used off of Craigslist from a lady who was down-sizing her home and it has been perfect in every way and was less than 1/2 the price of new, so deals are out there.
Be sure to negotiate the price or accessories with the dealer.

Watson

I don't know anything about it. You have gotten good ideas. I mainly buy new, no good dealers around me.

My wife purchased her Janome 9400 as a demo machine, trading in her 6600. She saved $1000 over what she would of paid by trading in her 6600 on a new machine.

That machine has had enough quirks, even after having it back for service once, that I think we would of bought new if we did it again.

That said, we've bought lots of used things over the years that have worked out great.

Jim

goodness i have a Janome 4800MC. I would love more throat space. I'd say go for it.