The problem is that he's been force-fed.

The guy at the reptile store misguided you and gave horrible advice. Force-feeding is a last resort option that takes place when the animal would die if it didn't receive some kind of nourishment. Force feeding is EXTREMELY stressful on ball pythons and often makes non-feeding issues WORSE than they are in the first place.

Spraying the ball python with vita-spray is worthless - they don't absorb anything through their skin and your just spraying your money away. Did the guy at the reptile store tell you to do that too?

Feeding problems, especially in young balls, are almost always related to husbandry/care issues.

What exactly is your cage setup? Describe in detail. Hides, type of enclosure, bedding, water bowl, everything.

What are you using to measure temperature and humidity?

What are the temperatures on the side of the cage with the heat source and the side of the cage without? (usually referred to as the "warm" and "cool sides", respectively)

What is the humidity level?

Answering these questions will help us get started helping you.

PS. Don't listen to another word the guy at the reptile store says.