Hello yepdom, the refund rate is a lot depend on a product and category. For example, books and media have lower returns rates as they are generally well-described products that the customer knows what they're getting.
The average return rate may vary from 5-15%, and you should decide for yourself what percentage is acceptable for you. For my products, this number is about 3-5%.
Of course, Christmas makes a huge impact and a lot of Christmas purchases which were bought with discounts are being returned up to now, so it's better to assess median refund rate for 6-12 months.