Yes, discounts or cash back rewards are not taxable. To exclude them when they are included on Form 1099-K, follow what @DawnC describes. Otherwise, the Cash Back Rewards will need to be included in the expenses.
To enter the discounts/rebates/rewards so they are subtracted in TurboTax:
- Go to Self-employment income & expenses and Edit/Add
- At Your 2020 self-employed work summary, select Edit
- Scroll down to EXPENSES and click in the lower left hand corner, Add expenses for this work
- Scroll to Other miscellaneous expenses select the toggle, scroll to the bottom of the page and click Continue
- Enter a Description in reference to the tax form if you wish, such as Form 1099-K Cash Back from Rakuten, the amount, and Continue
[Edited 01/25/2021 | 12:47 PM PST]