Service Connect Sales Order Problem

Hi Everyone,
I am working on a Service Connect right now that's proving very difficult. Here is the situation:

We have a Customer that is submitting Sales Orders via email, in an attached text document. The Service connect, in its first version, works perfectly fine. It basically strips the info (part number, part price, etcÂ…)and plugs it into a Sales Order. At that point a user has to hit confirm. If there is an invalid part number it skips over that one so the user has to look at the attached xml file to see if all the line items were entered properly and if not she has to manually enter them.

Here's what I've been tasked to do:

Somehow flag a part number that is invalid instead of skipping it. For instance, when she hits confirm, pop up a message that says "Sales Order: xxxx is has an invalid part number" and/or send an email off to her telling her the same thing. It should not let her confirm invalid parts or price but stop her there.
If the part number is valid, I need to check the price and do basically the same thing.
If all is good I just need the order to go through.

I have tried using BPM's, customizations and Service Connect to accomplish this and think I have gotten awfully close to getting it right but have had no luck at all. I am basically out of ideas at this point and we are trying to go live ASAP so any help or insight into this anyone can offer would be very much appreciated.