Building a Black Friday offer without killing your margin
A sitewide discount is easy to set up and easy to regret. Plan the offer around margin first.
Work out your margin
For each product, subtract cost, shipping, payment fees and expected returns from the sale price. That tells you how much discount you can afford, if any.
Add value instead of only cutting price
Bundles, a free gift with orders over a threshold, or early access for subscribers can move more orders than a deeper discount. Alex Hormozi's $100M Offers is a useful read on making an offer more valuable without cutting the price.
Test it before the weekend
Set up the discounts on a test order, including combinations you don't want to allow.