Get if you like it.
No, it not normal for bass to just sit on the bottom of the tank.
Yes, it normal for a lighter shade on the tail.
It's stressed. Could be the tank, water, pictures, traffic and so on. All I can tell, it's really stressed out in those pictures. Looks heathy other then that.
This will be a tough call. I had a jardini with tank mate before and it worked. I have no idea how big your Jar is or his temperament is with tank mates. It could work or it might not. As for the bass and introducing it to your tank if you do decide to buy it, I would do a 1 hour drip. IMO/IME pbass are more sensitive to ph shock then any other cichlids I have ever owned.