In case you want to use android apps on the device, I'd recommend not to get the Jolla 1 at this point. The last times I used those, it was a bit of a pain, because they were killed before even loading properly (not enough RAM). Could have something to do with play services installed on the device I used, though, so YMMV.

Otherwise:
Of all Jolla 1 I've used in the past, most defects (apart from batteries losing contact, which can be fixed with some tape) were either in the screen (discolourations and/or dead pixels) or with the vibration motor (can be replaced easily with a really cheap one from ebay for a few pennies – someone from here send me one of his spare ones, because they usually sell in batches).
So I'd recommend to get sharp pictures of the powered-on device if you find a used one.

cheers!