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.