I generally have 2 embroidery machines going at the same time, a big one and a little one, and I don't have a business, I just do a lot of embroidering, so I can understand the "secondary" machine comment.
I have sold 2 embroidery machines in the last few years - a Brother 8500D and an Innovis 4000D. The gal who purchased the 8500 was able to pick it up and I sat down with her and "trained" her on the machine. The gal who bought the Innovis wasn't able to do that, her sister picked it up and delivered it to her, she lived 8 hours from me. I used both machines a lot but I had them both serviced before I sold them to be sure everything was in good working order, and I provided the buyer with the receipt of service as proof. If you, or anyone else, is going to take a chance on a pricey used machine like this one, the seller should have it serviced before you buy. It's just the right thing to do.