呵呵,长点但条理清晰些:

Dim sh,fh, ss,fs As string
Dim sk,fk As Boolean
dim dr1,dr2 as datarow
dim Dt as datatable = datatables("基本资料")

sk = e.datarow("收货_抵扣")
fk = e.datarow("发货_抵扣")
sh = e.datarow("收货_单位")
fh = e.datarow("发货_单位")
ss = e.datarow("收货_税号")
fs = e.datarow("发货_税号")
dr1 = Dt.find("[客户名称]= \'" & sh & "\'")
dr2 = Dt.find("[客户名称]= \'" & fh & "\'")

If e.DataCol.Name = "收货_单位" Then
    if dr1 isNot nothing Then
         e.datarow("收货_税号") = IIF(sk = true,"+","") & dr1("税号")
    Else
         e.datarow("收货_税号") = Nothing
         e.datarow("收货_抵扣") = false
    End if

Elseif e.DataCol.Name = "收货_抵扣"  then
    If sk = true then
        e.datarow("发货_抵扣") = false
        e.datarow("收货_税号") = IIF(ss.substring(0,1)="+","","+") & dr1("税号")
        e.datarow("发货_税号") = dr2("税号").Replace("+","")
    Else
        e.datarow("收货_税号") = dr1("税号").Replace("+","")
    End IF

ElseIf e.DataCol.Name = "发货_单位" Then
    if dr2 isNot nothing Then
        e.datarow("发货_税号") = IIF(fk = true,"+","") & dr2("税号")
    Else
        e.datarow("发货_税号") = Nothing
        e.datarow("发货_抵扣") = false
    End if

Elseif e.DataCol.Name = "发货_抵扣"  then
    If fk = true then
        e.datarow("收货_抵扣") = false
        e.datarow("发货_税号") = IIF(fs.substring(0,1)="+","","+") & dr2("税号")
        e.datarow("收货_税号") = dr1("税号").Replace("+","")
    Else
        e.datarow("发货_税号") = dr2("税号").Replace("+","")
    End IF
End IF