Do you have anything else in the row that might help to find duplicates? Address? Phone? DUNS number? federal tax id?

What makes a business unique? Costco has a lot of stores. Is each one unique or should there only be one row for the parent company alone?

If you have only the name to go on, I'd recommend you hire one of the services who do this for a living to help clean up your data. The rules for this are extremely complex and most folks who do this don't guarantee that they will ever get to a 100% cleanup. Dun and Bradstreet has a service for this (I don't work for them) and I'm sure there are others.