How do you approach an unknown fish player? I know it depends largely on the player pool/ stake, but from experience an unknown fish in my 50-100nl hudless site player pool is on the passive and nitty side. About 10% of them being spewy/bluffy, 10% being whales and the rest of the 80% is on the passive side, with about 60-80% of those players within that 80% pool is capable of occasional bluffs and spews.
I could be wrong due to bias and no database , but that's my estimate.

Also do you player pools of fish drastically change in different stakes?

I saw in 200nl video that the coach bluffed catch rivered 2nd pair ,bb iso (coach) vs sb limp second pair on Q 10 4 2 J, vs a fish 2/3rd lead , after the the coach cbet flop, and checked turn. And the fish was bluffing with 86s (a wide call vs cbet). In my stakes , I would see this being pretty underbluffed, as everything gets there.

From this video and watching other higher stakes player, I think that as the stakes get higher 200 and up the average unknown fish is largely a spewy and bluffy player (about 75%). Which makes following a coach's reads on an unknown fish an error , if you player pool plays different.

So how should a player on a different site approach profiling an unknown fish? In some spots it's hard to estimate the average range based on the percentage of each fish player type in the pool vs an unknown fish, for example on a river bluff catch where you know about 30% of the pool is never bluffing , 10% of the pool overbluffs by alot , and 40% is maybe capable of bluffing .