I think we would need to see photos, but it sounds like corrosion.  If this were an old Mark VI or 10M or such, I could understand maybe purchasing a horn that has some corrosion.  But the Cannonball is a Taiwanese horn, and there are so many good used Taiwanese horns available, that I would not buy one that might have corrosion.

I don't know your budget, but here is one possibility:
https://www.junkdude.com/collections/saxophones/products/barone-mac-20rth-tenor-saxophone

Here is a second one:
https://www.saxquest.com/product/view/pristine-antigua-winds-black-nickel-tenor-sax-serial-st3035266-P12346 

Oh, and a third possibility (for a little more price):
http://www.2ndending.com/saxes.html

It seems like those green spots are lacquer loose due to a little gastric accid expulcion from the seller or previus player not because the sax model or brand name. I personally have being traveling  to USA Europe, Central and South America for about 25 years with latin bands and i have a sax specialist in NYC, Mendelsax.com. This is a person who really care about sax players mouthpiece and their instruments. Is a person who pass thrue a serious situation with his career as sax player but had the logic sence an level of understand the medicine and technology world, enough to understand how the organisim work in communicacion with the instrument and how the instrument must be to help the players show up their best performance. There is no many tech with information on that direction.This gentleman should help you with any thing related to saxophones. " Good but good".

Hi Mason,

The Hotspur has a satin silver plated bell, and if the sax is pretty new then it's probably because the owner simply hasn't cleaned it so it's dirty and tarnished. If that's the case, it should be pretty easy to remove and polish up.