GoldMine has really good duplicate checks on the entry of new records (checking on one or combination of fields) and also the merge-purge feature. Here’s a quick SQL Query you can run in GoldMine (go to your Filters and Groups, and click on the SQL Query Tab) to check on duplicate Company Records.
select company from contact1 group by company having count(company)>1
If the query finds any, then use GoldMine’s Merge Purge feature to remove them.
NOTE: Keep in mind that there are some organizations that prefer to have Duplicate Company Records, for example; companies with different office locations, they may create multiple contact records for the same company, with different address information.