The issue is there is a database with around 20k customer records and I want to make a best effort to avoid duplicate entries. The database is Microsoft SQL Server 2005, the application that maintains that database is Microsoft Dynamics/SL. I am creating an ASP.NET webservice that interacts with that database. My service can insert customer records into the database, read records from it, or modify those records. Either in my webservice, or through MS Dynamics, or in Sql Server, I would like to give a list of possible matches before a user confirms a new record add. 

So the user would submit a record, if it seems to be unique, the record will save and return a new ID. If there are possible duplications, the user can then resubmit with a confirmation saying, "yes, I see the possible duplicates, this is a new record, and I want to submit it". 

This is easy if it is just a punctuation or space thing (such as if you are entering "Company, Inc." and there is a "Company Inc" in the database, But what if there is slight changes such as "Company Corp." instead of "Company Inc" or if there is a fat fingered misspelling, such as "Cmpany, Inc." Is it even possible to return records like that in the list? If it's absolutely not possible, I'll deal with what I have. It just causes more work later on, if records need to be merged due to duplications.