Looks can be deceiving especially with a subtle morph like a YB. You wouldn't be the first or last person that bought a snake advertised as a YB to find out later that it wasn't. Plenty of normals look like YB but there are differences between the two.
It looks like it "could" be a yellowbelly but I would ask for belly pictures or buy one from someone willing to take pictures to satisfy you 100% on the genetics.