Special Situations and At-Risk Populations
Some guests need extra care. Pregnant guests should be informed that no amount of alcohol is known to be safe in pregnancy; a server may decline to serve and offer alternatives. Guests taking medications, especially those causing drowsiness, may be impaired faster. Guests with known alcohol dependence may be at risk of severe withdrawal and should not simply be cut off without attention to their safety. Younger-looking guests, guests celebrating 21st birthdays, and groups buying rounds all deserve careful ID and pacing checks. Guests who arrive already intoxicated must not be served - arriving drunk is itself a reason to refuse.
Other situations: private parties and special events where alcohol is served still require ID checks and monitoring; guests who appear to be buying for minors (a "shoulder tap" - asking a stranger outside to buy alcohol) should be refused and reported; and guests who become aggressive, or who are clearly planning to drive, need intervention. If a guest is or becomes a minor, do not serve. If someone appears to be in medical distress, call for help.
Traps: assuming a pregnant guest "knows" and doesn't need to be told; assuming a group will handle an impaired friend; and missing third-party purchase attempts.
Worked example: a young adult outside asks a customer to buy a six-pack for them. The server refuses the sale to the adult and notes the attempt. Rule of thumb: when a situation is special, slow down, get a manager, and default to not serving.