Though not advised by many and some manufacturers...2 sharp ended screwdrivers can often pry them out...you just have to be careful not to damage the pump body.
You can also drive some screws into the rubber to get a better grip with vice grips and use brute force pulling...but before that try soaking the shaft with penetrating fluid and gently tapping the impeller brass with a punch to loosen it.
While they all can be hard....I haven't had one in a long time fight me too badly...but then mine are usually replaced or at least removed every 2 years.
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