Is there a way to compare data from two workbooks?

Question: I am a printer that does a lot of mailing. I import data from excel into mailing software, I process the data and then export to excel. Most of the time it's simply a mailing address along with mailing items (Barcode, sort order number, tray number.........) Occasionally I'll have a bunch of data to import like from a theater company with show night, seat numbers, season ticket price total........I just did a mailing like that last week. The data imported in OK. But when I exported the data 14 out of 1700 records had improper data. This is the first time this has ever happened. It appears to simply an export error. This is unacceptable to my client. So the question is would there be a way to compare data from two workbooks? The columns may not match, but there would be a customer number that could be the key. Feel free to ask for clarification.