At a previous employer, as soon as I finished a task, my manager would go on assigning me cumulatively more work than what I was supposed to do. Not surprisingly, they could easily sense my reluctance to take any more of it, so they would try to sweet-talk me into doing it, say, "You always do a good job!" and the like. Most of the time I didn't know how to respond to such wily tactics, which I would describe as quite insincere and exploitative.