Dim dtFirst, dtLast As Date
dtFirst = DateSerial(Now.Year, Now.Month + 1, 1)
dtLast = DateSerial(Now.Year, Now.Month + 1, Date.DaysInMonth(Now.Year, Now.Month + 1))
Cmd = New OleDbCommand("SELECT Seller, Service, Total, DueDate FROM Transactions WHERE Name=@givenBuyer AND DueDate BETWEEN [b]#[/b]" & dtFirst & "[b]#[/b] AND [b]#[/b]" & dtLast & "[b]#[/b], Conn)
Is better.
I'm not sure how this snippet handles December, but it's some first steps at least.
HTH
Kejpa