I've got a 16C in very good condition. It passes its keyboard and self tests. I don't have the case, box, or manual, and if you look closely there is a very small scratch on the brushed aluminum panel to the left of the display.

Having never sold a calculator before, I wonder if I need to address the case or manual before I list it for sale? Would there be much interest in this calculator?

Hello.
If you put your 16c on e-bay, it will sell. All of the HP voyager series were great machines, and always gererate bids.

Right now I count 5 of them for sale on E-bay, and they all have bids (or buy it now prices) ranging from $61 to $199.
Best regards, Hal

As Hal said, it will definitely sell! No worries about not having the case, manual, etc.

I know when I buy calculators (from eBay or wherever), I always appreciate clear pictures & thorough descriptions. A shot with the self-test results visible is always nice, and if you can zoom in enough to show the small scratch, that's nice, too. A mention the battery compartment's clean is helpful as well. Limiting your listing to a blurry picture with a scant description is a sure way to limit your final price!

To amplify further: two pictures of the display showing the two different self test results, as well as an overall picture of the back of the machine and the front. The case is not an issue as any Voyager case will fit (and there are plenty of those on eBay), and manuals are pretty easy to find as well.
Good luck
Pierre