how exclude item in combobox based on word in another column

Leap

I think I understand your question and feel you have two mistakes in your code- you were NOT checking a single cell was equal to "cust" (before checking if the item had been added to the ComboBox list) and need to use COUNTIFS to add a second criteriia to the count (i.e. that C&i is "cust" as well as D&i). I've declared a new variable Only so you need to change it in one place only.  I've made the changes in bold below (and in the attached file):

Private Sub UserForm_Initialize()
Dim i As Long
Dim Only As String
' say what C should be for an item to be added to the ComboBox
Only = "cust"

For i = 2 To 10
    If Range("c" & i) = Only Then
        If WorksheetFunction.CountIfs(Range("D2:D" & i), Range("D" & i), Range("C2:C" & i), Only) = 1 Then
            Me.Combobox1.AddItem Range("D" & i)
        End If
    End If
Next i

End Sub

Hope this fixes it.