If someone is unsure about the halal nature of their income, they should:

1. **Seek Knowledge**: Learn about Islamic guidelines on earning halal income, focusing on what is permissible and prohibited.

2. **Consult a Scholar**: Seek advice from a knowledgeable Islamic scholar to assess the nature of the income.

3. **Evaluate and Adjust**: Analyze their work or business practices. If any part is questionable, they should seek alternatives that align with Islamic principles.

4. **Make Tawbah (Repentance)**: If past earnings were not halal, they should repent and commit to earning in a permissible way.

5. **Purify Wealth**: Consider giving charity from doubtful earnings as a way to purify their wealth, although this doesn’t make it halal but can be a step toward rectification.