In my opinion I would say no. The handles may be adequate maybe not, but I see no way to guage or measure pressure. It says it does online. I would find out how often it was used as well. You need specifics to safely use one. Here is a comparison with reviews.
http://www.amazon.com/Mirro-92122A-...washer/dp/B000RNH7PQ/ref=cm_cr_pr_product_top
This one is brand new and cheaper as well.
When I studied the best option. I loved this one. She is well made and american craftmanship too.
You might be able to find one elsewhere for less.
http://www.amazon.com/All-American-...id=1377195569&sr=1-2&keywords=pressure+canner
From what I could see the gauge is in the handle. The site I looked at did not give a view. Now if the one on CL has a rubber seal like the presto , which used to have it might be no good. They must be oiled and maintained.
I did not find a 23 quart Mirro but did find a 22 quart. Perhaps she can no longer get a seal for the 23 quart?
It seems to me you can buy a new one and not have to take the extra pots you don't need. A Presto is only $74 free shipping. The water bath canner can be had for at least $39 new. So $100 for a used set is to much.
If you can find a rubber seal for the 23 quart AND if you offer her less than she's asking and get a better deal then you might consider it.
Personally I'd go with new. A pressure canner is not something I'd mess with used. I also like the on top gauge and rocker models. I would not be likely to can anything that needed extremely high pressure for too long.