Why are there duplicates in my Zendesk Sell account?

Question

How do I avoid duplicate leads and contacts in my Zendesk Sell account, and clean them up when they occur?

Answer 

A Sell admin can choose a strategy to avoid duplicates for the account in Settings > Data > Duplicate Management. This will automatically identify duplicates if records have the same name and either the same email or phone number. 

The duplicate management strategy prevents duplicates when you import a new CSV file or when you convert leads to contacts. The Duplicate Management settings do not scan information added to the account using the API or other third-party integrations.  To customize your strategy, see the article: Managing duplication settings.

Finally, if you want to clean up duplicate leads, contacts, and deals in your account, see the article: Merging leads and contacts.