What "refund guarantee?"
There is a 60-day no questions asked money back guarantee on the desktop version (installed on your own computer from a CD or download).
The accuracy guarantee guarantees accurate calculations, and if you are assessed a penalty or interest for an inaccurate calculation, Turbotax will pay the penalty or interest. You always owe your own correct tax, whatever it is. If you are getting a larger refund, you can't make a claim against the accuracy guarantee.
Turbotax is not guaranteed against user mistakes. I have not yet seen any problem with the recovery rebate that was caused by a program error (although there might be cases I don't know about). All the recovery rebate problems I have seen so far are the result of user error.
