Service becomes exploitation when one person’s goodness is treated as unlimited supply.

Every group has one person who always says yes, and groups quietly organize themselves around that. What started as their good nature becomes an expectation, then an entitlement, and the generous person is treated as infrastructure rather than as somebody making a choice each time.

If you are that person, one refusal will tell you a great deal about how it is being received. And if you rely on somebody like that, check whether you have thanked them recently or simply assumed. Goodness taken for granted is how it eventually runs out.