There's a certain level of trust between miners and pool operators.  Pool operators - at least the honest ones - are transparent with their operation.  For example, you'll see published generation addresses, coinbase signatures, etc.  That's not to say there aren't bad actors out there.  Scammers will get people mining on their pool, only to steal the block reward.  They don't last long, but the damage is done.

Most mining hardware interfaces will indeed show the highest share found, which is a good indicator of whether or not that gear found a block.  Also, most miners are very quick to point out any discrepancies.

So... is it possible?  Sure.  But those pools don't last long once people realize they're being ripped off.