I. Always inspect before you buy- many of us on here have learned that the hard way.
now you've learned.
II. If you're just starting out, I'd return it if you still can, advise that they quarantine/destroy it, and start fresh with a more promising plant- and avoid discouraging results from this one.
III. I am not sure what this is- could be fungal/bacterial, could be a virus. I'm leaning towards bacterial/fungal. If it's a virus, it will affect the new leads as well. Either way, I think it would be best to get a healthier plant that will boost your confidence, instead of being a downer.