Usually, if the item is overweight or is to be shipped overseas, UPS and USPS modules won't work. This contribution is two modules in one.
1) The first RFQ allows customers to select 'Request Quote'as a shipping method. By default, this is a $0.00 charge added to the price (You can add a quote fee). You may then contact the customer via email with correct shipping quotes.
2) The second module RFQ2, allows the customer to pay for the item via normal methods, or select request for quote, pay nothing, and await your response.
Oscommerce works as a catalog and referral, but the final shipping and payment is done manually through your brick-n-mortar store via, phone, fax, mail, email, etc.