$dbh=$db->prepare("SELECT nvl(mb_award,0.00),
                          nvl(mb_accept,0.00)
                   FROM Items
                   WHERE itemnum=? AND seller=?
                         AND closef='1'");
$dbh->execute($form{'item'}, $fdnum);
my ($mb_award,$mb_accept) = $dbh->fetchrow_array();

my $mb_amount_disp = $mb_award > 0.00 ? $mb_award : 
                        $mb_accept > 0.00 ? $mb_accept :
                           0.00; # Assume you have negative values