TurboTax has a 100% Accurate Calculations Guarantee. However, this does not cover user errors such as omissions and reporting inaccurate information on the tax return.
See this TurboTax support FAQ for the Calculation Guarantee - https://ttlc.intuit.com/turbotax-support/en-us/help-article/account-management/turbotax-100-accurate...
And this for submitting a claim - https://ttlc.intuit.com/turbotax-support/en-us/help-article/intuit-account-billing/submit-claim-turb...
