Determining ethical boundaries can sometimes be a challenge, since ethics is both based on individual beliefs as well as societal standards.
Would receiving a holiday gift from a client be considered bribery? Would it be wrong for a person in a position of power, like a mayor, to ask a bank manager friend for a personal loan? On a more practical level, is it unethical for a cashier to provide a coupon to a customer who did not have one at the register? Is it unethical for someone to complete a timesheet recording eight hours of work, when they left 45 minutes early?