Our algorithm uses a mix between known folder directories and extensions to determine which files to transfer over. The program moves over all documents, pictures, videos, and audio extensions plus many, many more (minus things like system files e.g. ".dll").
Our service will also look in the root directory (and all over the drive) for files to transfer (e.g. "C:\"), so you can be confident the data will transfer if it exist. To this date, we have never had a customer that stated a specific file was not moved over (even if so, they still have their old drive that has all the data on it untouched). Try the FreshStart service on every possible customer, just for the time-savings alone (versus looking for the data manually). All of the files we transfer go exactly into the folder tree/structure they were in on the old drive, so the customer will know exactly where all their files are. Lastly, we also make sure no viruses are transferred over, which speeds up the process even more.
If you notice (or your customer notices) a specific file was not transferred, please let us know and we will add it to our long rules list. We can make those changes extremely fast and easily.