How do I hide products from certain customers?

You control this under Products & Pricing → Product Visibility. There are two ways:

1. Set your default. Choose whether products are Visible by default (everyone sees everything unless a rule hides it — recommended) or Hidden by default.
2. Add rules with groups. Create a Customer Group (e.g. "Cafés") and a Product Group (e.g. "Wholesale-only lines"), then on Overview click Link Customer & Product Group to show or hide that product group for that customer group.

To hide a single product from a single customer, do it at the product level in Price Exceptions instead. Use groups when you want the same rule across many customers or products.