For those that have the Dual Pricing - Wholesale Pricing module, you can disable shipping with this code
Code:
// bof: Disable free shipping for wholesale customers
      if (!IS_ADMIN_FLAG) {
        $chk_discount_group_sql = "SELECT customers_whole FROM " . TABLE_CUSTOMERS . " WHERE customers_id = '" . $_SESSION['customer_id'] . "'";
        $chk_discount_group = $db->Execute($chk_discount_group_sql);
        if ($chk_discount_group->fields['customers_whole'] != 0) {
          $this->enabled = false;
        }
      }
// eof: Disable free shipping for wholesale customers