It's sort of hard to define that exclusive rule though. The first rule would be if it's only item A then use the lower handling rate. The second rule is if it's anything else or anything else including item A then use the higher rate. I'm not even sure how to make these exclusive without a case. Your extra column would work. I guess the advantage would be that the handling charge could be changed for items just by changing the database but I will also have to add that data field in and track it all the way through to checkout.
It's hard for me to keep my hands out of the code. I have to figure out how to manipulate the interface to get what I want and then I still find myself going to the code to check the result, at which point I think to myself why didn't I just code this the way I wanted it in the first place. LOL