If you have a Federal refund and choose direct deposit, how the refund money is routed depends on how you chose to pay the TurboTax fees.
If you have no TurboTax product fees, or if you pay the fees upfront with credit/debit card or a prepaid debit card you can buy in a store, then the refund money goes directly from the IRS to your bank account (or to a prepaid debit card if you are direct depositing to a card.) In this circumstance no third-party company is involved.
On the other hand, if you do not pay your fees upfront and instead choose to pay them out of the Federal refund, then the refund goes first from the IRS to an intermediary bank where the fees are subtracted. That intermediary bank then sends the rest of the refund to your bank (or prepaid card.) The company that administers that process is SBTPG (Santa Barbara Tax Products Group.) If you choose to pay your fees out of the Federal refund, there is a 39.99 service fee (44.99 for California filers), and the refund will go through SBTPG's bank first.
