Cant say for sure its sex, but it looks healthy and is probably way better looking in person.
To be fair to the fish, its on black gravel, in a dirty 55, in pics taken by someone that probably isnt a photographer and the pics have been shrunken down by craigslist, which changes resolution/colors a ton. Ask him for more pics if you can.
The bottom pic looks like something from fosters and smith or somewhere...doesnt even look like the same fish. He might have it there for reference.
Ive seen several Umbees from Don and they were beautiful...so Ill bet it is as well.