Conditional Formatting Formula - highlight cells with different values within a criteria

Hi All,

I have a sheet with a column that lists the client account numbers for people who made online purchases over a given period of time (user chooses day, week, month etc). Every transaction for the time period is listed and some clients may have purchased more than once. Another column is for transaction method - AMEX, M/CARD, DEBIT, etc.

I would like to conditionally format the transaction method column to highlight all transaction entries for clients that have used more than one transaction method. Only transaction method needs to be highlighted. The result should look like the image and must work when sorted in any way. Excel sheet also attached for reference.

Is this possible with just conditional formatting?

Thanks in advance for any assistance!

David