Setting Up a Dedupe System for Customer Company Tables

Hello everyone, I'd like to set up a table of Companies that are currently customers or already in the pipeline and then have future company tables dedupe with that original table. Has anyone worked out a good way to achieve this yet? Example: if all of my customers are in a table 'Customers' and then I import a csv of company data that has a row in common with Customers i'd like it thrown out of the new table automatically