At first it looks like a possible blockage but you say it's been this way for a long time(?). That kinda rules out that theory.
Does the snake defecate normally?
From the discolored scale I would say it might be some kind of injury or possibly a birth defect.
The first photo shows that this, whatever it is, is not asymmetrical.
That does it feel like? What I mean is, is this area hard or is it the same as the rest of the belly?
No offense with this next question but can you trust the Pet Shop? They may not have taken it to a Vet.
Nice looking snake. Best of luck.