Custom Field Radio buttons can be set up as shown in the example below - where one or other option is chosen: 

The Radio button allows you to set one choice (option) as the result so therefore differs from a checklist where multiple choices can be selected. 

How to Set up a Radio Button Custom Field: 

1. To set up a Custom Field as a Radio button format please go to the Settings icon as shown below: 

2. Click on the 'Global Settings' tab:

3. Click on 'Add New' to add a new Custom Field row: 

4. This creates a new Custom Field row as shown below:   

5. Enter your Custom Field heading (as shown in the example below): 

6. Change the format drop down from 'Text' to 'Radio' as shown below: 

7. Click on 'Update Settings' to save and go back into the Global Settings page:

8. A new field has now been added as shown below: 

9. Enter into this field the options such as 'Retail' and 'Professional' ensure that the options are added in the following format with the comma (,) between each one as shown below: 

10. Click on Update Settings to save.

11. Now back inside your contacts record you will see the Custom Field has been added as a Radio option:

12. Just select the appropriate option and click on 'Update' to save: