1. Sort the List by Customer Name by selecting a cell in column C (see screenshot)
and clicking Sort Smallest to Largest icon (in Data tab).
2. Select a cell in the List and press Ctrl+Shift+* or press Ctrl+A.
3. Select Home -> Conditional Formatting (in Styles Group) -> New Rule.
4. Select Use a Formula to determine which cells to format.
5. In Format values where this formula is true enter the formula =$C1>$C2,
click the Format button, select the Border tab, in Border section choose a color
and click Underline, then click OK twice.