How to add discounts by product category for a customer?

In Admin, navigate to the Customer Page and go to the Category Discounts tab. You can define discount levels for any selection of categories on your site:

Discount rules

A product can be allocated to multiple product categories. Or a customer may already have a general rental or sales discount defined. These are the rules that apply:

1. Category discounts take precedence. If the product...

• ... matches at least one category, then the category level discounts will apply
• ... does not match any discount category, then the general rental or sales discounts may apply if they are set (help article here)

2. The highest category discount will apply if the product matches on multiple categories
3. The maximum discount value is 100%

Category discounts apply to both rental and sales products. If you need separate discounts, then simply create dedicated separate categories as required.

Tip: Product Categories can be defined as "children" of other categories ("parent"), on the product categories tab in admin (under Product in the main menu), and this can help you be very granular in defining where the discounts should take effect.