How do I set custom pricing for a specific customer?

Think of it in two layers — set the base with a price list, then fine-tune with price exceptions:

1. Start with a price list (the base). Assign the customer a price list to set their general pricing level. You can apply it when adding the customer, or from the customer record.
2. Customise with price exceptions. For products that should differ, go to Products & Pricing → Price Exceptions, find the customer (or add them with +), and set the custom price per product. Use Import to do many at once.

Both apply automatically when the customer orders.

See also: "What are price lists and how do they work?" and "What is a price exception?"