FinalFormula

1. Create a new formula called FinalFormula.
2. Type the following in the Formula text box of the Formula Editor:

If ({customer.CUSTOMER NAME} [1 to 2] = "Bi" and
ToText({customer.CUSTOMER ID}) [1] = "6") or
({customer.CUSTOMER NAME} [1 to 2] = "Ro" and
ToText({customer.CUSTOMER ID}) [1] = "5") Then
    "PREFERRED CUSTOMER"
Else
    "DOESN'T FIT CRITERIA";

3. Place the formula where you want it to appear in the Details section of the report. You can now delete all other formula fields from the report. See Deleting formulas.

You can use this same process of condition-by-condition testing for any formulas as a means of systematically checking them.