In this situation , unless you want to risk
1) loosing the money you paid to buy it
2) having it confiscated
you are better off not reporting it ( 1 and 2 will happen to you most likely if the boofocrat has a bee in his or her bonnet ) as well as maybe the seller being prosecuted ( doubt it for one or two or a small group of reptiles illegally "acquired and sold" ) .
I'd just keep them "off the books" if you've bought them in good faith and no licence number was provided and you don't see proof it's "REAL" and didn't see their rego number or drivers' license and you REALLY want the animal.
But what about the risk?
I don't know if inspections are common or not, but even if they're not - as
@Flaviemys purvisi pointed out - if the seller was caught they may be quick to give up all their customers for a lighter penalty.
What really needs to be considered here is the possibility of a criminal conviction if the original poster is caught.
My concern about keeping a clean slate hasn't been the monetary penalty, but criminal conviction. Even if the punishment was as low as $50, if I want to get into other countries in future, or get a job in many different areas that single criminal conviction could stop a lot of opportunities that I otherwise may have had. And I could probably also forget about ever getting a wildlife permit/license again.
I have a friend who I know can't even go to the USA on holidays (who hold senior citizen cards now) because of a single silly thing they did when they were a teenager. We're talking nearly half a century ago.
That's not to mention the risk of losing the rest of collection (via losing their license), and not being able to get a wildlife license again if they were caught.
It may be a small and unlikely risk of getting caught - but it could have serious future consequences moving forward if they were.
Personally it wouldn't worry me which direction the Original Poster takes - provided they are aware of all the risks and makes an informed decision.