Adding Two Cells / Different Rows Based On Duplicate In Third Row

I have a sheet which has the following Columns:

Name..........Sales..........Returns..........Net

These are columns B,C,D,E,

Because the data is imported, it shows one row for the person's sales and another for their returns like this:

Dave...........100...............0...............(Blank)
Dave..............0.............-20..............(Blank)
Fred............200...............0...............(Blank)
Andy..............0............-500..............(Blank)

What I am trying to do is get the net sales of 80 in either of Dave's rows in the Net column, then I can hide the duplicate row. However, this is complicated by the fact that names without returns, (like Fred in this example,) do not have a second row. (This also applies to those names without sales, but with returns, like Andy).