it really depends on what you need to find out about the result
if you need to test if a the row/data exists then just check for null and
you need to test if the row/data exists and has a valid value then try the
following

///
object result = cmd.ExecuteScalar();

if (result == null)
     return "Customer not found";
if (result == System.DBNull.Value)
     return "Customer found but name is null";
return (string) result;
///