Any chance you would ever sell it on?

I would be wary about buying a Panerai with no box and papers. The box isn't some flimsy cheap affair like you get with a Tag Heuer - it's pretty substantial and good quality. Why would someone throw that away? If you can afford a Panerai, you surely have a house/apartment that has enough cupboard or loft space to put a Panerai box.

It might be a genuine Panerai, but I would be worried about it being stolen - both legal and moral issues with buying a stolen watch.

And the other problem is what if you ever want to sell it on? Any buyer is going to have the same concerns you have now.