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 deduplication strategy for the account in Settings > Data > Duplicate Management to automatically identify duplicates if records have the same name and either the same email or phone number.  

The deduplication 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.  See the article: Managing duplication settings to customize your strategy.

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