When I'm interested in buying a used machine, I bring my own supplies, just like SuzzyQ says, and I "test drive" it. That way I know that it works and if I have any questions, hopefully the seller can answer them. Rarely has the machine been serviced so I pretty much expect to take it in for servicing if something goes wacky but if I'm getting a really great deal, I don't mind doing that.
I've bought a couple "lightly used" machines, and they were just that. One was rarely used because the manual was missing when the gal bought it and she didn't know how to get a manual so she used it twice, put it back in the box, and there it sat for nearly 20 years. Another one I purchased was lightly used because the gal didn't buy the machine she really wanted, she compromised and then regretted it, so she ended up buying the one she wanted and sold the other one after only 6 months. Another machine I bought was "lightly used" because it was too high end for the buyer, she just couldn't figure it out, so she returned it to the store. That has been my primary sewing machine for the last 25 years. Lots of reasons a machine is "lightly used".
If you have a dealer in town that that fixes machines, they can probably service your machine. I have a variety of machines and my local dealer can service them all, high end or low end. And I live in a small town. You might want to check that out before you consider buying the Pfaff.
I own an older mechanical Pfaff and I owned a Pfaff Tiptronic at one time. Excellent machines.