I bought a used HQ 16 (slightly older model than the Sweet 16) about a year ago and just LOVE it for large quilts! I have it set up as a "sit-down" and it works great!
As others have said, I'd ask why they are selling it. I think there are lots of good reasons; for instance, the lady I bought from had decided she really wanted to focus her work on small-ish art quilts and didn't need the 16" throat space the HQ 16 offers. I went to her studio to try out the HQ 16 and saw a lot of her work, so I knew that was true.
Be sure to try it out before buy. I did, and was happy with how it performed. Since I'm using it as a sit-down model, it worked very similarly to my DSM, but had much more throat space, and the transition to using it was fairly easy for me. The first thing I did when I got it home was a queen size quilt for my daughter-in-law for Christmas -
http://www.quiltingboard.com/picture...d-t164909.html . I did a couple of practice feathers and then started right in on the quilt!
Here's my posting about how I set it up as a sit-down model using an existing table in my studio, (not the special Sweet 16 table):
http://www.quiltingboard.com/picture...e-t165016.html
There were a couple of factors that made me particularly comfortable with purchasing this machine from a Craigslist ad. The first, and most important was that it had originally been purchased from our LQS/Sewing machine shop and had been serviced by them while the original owner had it. The second was that I was able to try it out and felt comfortable with it.
I don't know if you are interested in the new stitch regulator that HQ offers for sit-down HQ 16s, but if you are be sure its compatible with this model. I got to try out the stitch regulator at a quilt expo just a couple of weeks ago in Tucson, and didn't particularly care for it myself. I think it does an OK job, but I've been practicing my FMQ so much that I'm more comfortable with FMQ when I can manually control the stitch speed. One really nice feature that the HQ 16s have is that you can set the maximum stitches per minute at whatever level you are comfortable with for the piece you are working on. I usually start at about 60% or so and adjust from there if I want to.
This machine is relatively easy to use, not nearly as complicated as your Bernina button hole foot! (I have one too, and still have to read the directions for it if it's been awhile since I've used it.) With the Sweet 16 you have an on/off switch, a maximum speed setting, and a foot pedal, and away you go! Threading is essentially just like your DMS, and you have a tension dial for the upper thread, and a screw on the bobbin case, again just like your DSM.
Feel free to PM me if you have additional questions. I'm a happy HQ 16 sit-down owner!
I even tried out some really nice LA machines at the quilt expo, but decided I am quite happly with this setup and not inclined to go bigger at this point.
The price sounds good on this machine, and if it comes with the table, the price is fantastic! Try it out, and see what you think--you'll know if it "speaks to you" or not!