What Would Tell You That This Had Been Cleaned? 1802 Dollar

I too am still trying to learn and on some coins I can't tell whatsoever but my guess is the tiny striation marks on the obverse and reverse...? The ones that look like tiny little scratches. Someone else will know more though :)

I'm going to have to punt on this one too.

FWIW my first impression was yes, cleaned. Just too clean on both sides, and looks to have some rub marks/hairline scratches. Maybe a long time ago, or just a partial cleaning.

It's also in plastic which is where some of the scratches could be also.

Sorry to not be more clear in original post, but yes it was deemed cleaned by PCGS, I am just looking to learn what to look for, the hairlines would have been my guess...
Here are pics of the full slab

Mainly using this an example to see what I could learn for next time,
while the price is "a little steep!", finding a genuine one at a cheaper price that has good looks and details can be a challenge under $2000.

In my opinion, the way I would tell is that the toning is darker around the rim than it is in the center of the coin and in the fields around the portrait. The absence of this darker color in the center likely would mean that it was rubbed off at some point. More uniform toning across the entire coin would indicate that it hadn't been cleaned.

I tend to think of it as if someone crudely rubbed the coin to make it shiny. They would have been able to easily remove the dull/dark spots on the flat surfaces and would have had a harder time with areas that had a lot of complex features (nooks and crannies on the surface of the coin). Minor scratches across the surfaces could also be an indicator here.

This manner of thinking gets thrown out the window if the coin was dipped in a cleaner, versus rubbed with a finger or a cloth, however.