Using the following code AdvancedFilter is working except where the filter is
set to 'D' on a particular column the returned set contains all rows where
that column starts with a 'D' i.e. D, Dad, Dolphin .... I need the returned
to be limited to the rows where column contains exactly 'D'.

Sub AllColumnsOneCustomer()
' Page 227
Dim IRange As Range
Dim ORange As Range
Dim CRange As Range

' Since this is called from a button on Menu,
' first select the sample data sheet
Worksheets("DBSize").Select
' Clear out results of previous macros
Range("G1:M50").EntireColumn.Delete

' Find the size of today's dataset
FinalRow = Cells(65536, 1).End(xlUp).Row
NextCol = Cells(1, 255).End(xlToLeft).Column + 2

' Set up the Criteria Range with one customer
Cells(1, NextCol).Value = Range("D1").Value
' In reality, this value should be passed from the userform
Cells(2, NextCol).Value = "D"
Set CRange = Cells(1, NextCol).Resize(2, 1)

' Set up output range. It is a single blank cell
Set ORange = Cells(1, NextCol + 2)

' Define the Input Range
Set IRange = Range("A1").Resize(FinalRow, NextCol - 2)

' Do the Advanced Filter to get unique list of customers & product
IRange.AdvancedFilter Action:=xlFilterCopy, CriteriaRange:=CRange,
CopyToRange:=ORange
' Range("L1").Select

End Sub