Duplicates sneak in when the same person arrives through two routes, or when a step runs twice after a failure. Decide what makes a record the same before you build. An email address works for many cases, a phone number for others, and sometimes you need both. Search for an existing record first, then update it instead of creating a new one. Make steps safe to repeat. If a step runs again, it should leave the same result rather than add another copy. Run a regular check for near matches, such as small spelling differences, and merge them with care. How do you decide that two records are the same?