Customer blacklist: how to build it, share it with your call center, and use it without mistakes

Guilherme Rocha · 2026-10-07

Creating a customer blacklist is an essential strategy for mitigating risks and fraud in e-commerce. Below, I’ll walk through the steps to build, share, and use this list effectively.

Entry criteria

1. Define what counts as fraud: This includes chargebacks, nonpayment, and orders with fake or incomplete information.
2. Set an incident threshold: For example, a customer could be added to the blacklist after three fraud attempts or two chargebacks within a 6-month period.
3. Verify payment information: Use real-time data validation to identify fraudulent credit cards or PayPal accounts with a questionable history.

Normalized phone numbers and addresses

• Data normalization: Use validation tools to make sure phone numbers and addresses are consistent and correctly formatted.
• Formatting: Phone numbers should follow the +55 (XX) XXXX-XXXX format, and addresses should include complete details such as street, number, neighborhood, city, and ZIP code.
• Database: Build a database to store this normalized data and make it easier to look up later.

Form integration

1. Registration form: Add a verification system to the registration form that blocks sign-up attempts using information already on the blacklist.
2. Validation API: Use data validation APIs to cross-check information in real time and reduce the number of fake submissions.
3. User feedback: Let customers know why they were blocked without revealing the blacklist in detail, to protect their privacy.

Review

• Frequency: Set a regular schedule for reviewing the blacklist—every 30 days is a good interval. This helps keep the list up to date and remove customers whose behavior may have improved.
• Data analysis: Use tools like FreeSpy to monitor how the lists are performing and adjust the criteria as needed.
• Team feedback: Set up a channel for the customer service team to report new incidents and suggest changes to the blacklist.

Legal limits

1. LGPD compliance: Make sure data collection and storage comply with the General Data Protection Law. This includes consent and the right to access the data.
2. Transparency: Let customers know about data collection and the use of the blacklist in your privacy policy.
3. Avoid discrimination: Don’t include customers based on personal characteristics or sensitive information. The blacklist should be strictly related to purchasing behavior.

Implementing a structured customer blacklist minimizes risks and improves call center efficiency. What criteria do you currently use for your blacklist? Share some numbers!