Here's a step-by-step process for a typical sale:

1. Ask for ID – even if the customer looks older than 21, ask. Consistency reduces bias and sets a standard.
2. Check the ID – look at the photo, compare it to the person. Check the birth date. Feel the card—fakes often feel wrong.
3. Verify the date – is the ID expired? Expired means invalid.
4. Confirm the age – the customer must be 21 or older. If they're under 21, stop the sale.
5. Complete the sale – if everything checks out, you're good.
6. Refuse calmly – if the ID is bad or the age is wrong, explain why you can't sell. Don't argue; just state the policy.
7. Log the refusal – note the time, reason, and if you have it, the ID details (without storing sensitive info).

For online sales, you need a different process—typically using a third-party age verification service that checks public records or scans IDs. That's beyond this piece, but know that the same 21+ rule applies.