Try looking at this situation from a different perspective-- that of your customer. If the manager can make an exception for the reasons you stated, expediency, dollar value, etc., then why do you make the customer wade through the front line to get that service?
Instead, empower your front line to make common sense exceptions without involving management. This will make their job easier & more pleasant, and provide a much better customer experience. If the employee goes too far or makes a mistake, coach them on it in private afterward, but never undermine the employee in front of a customer.
Hope this helps.
Geri
www.radiosophy.com