They don't expect to need a lot of bug-fixing and assistance. For example, they might be willing to work around bugs rather than get them fixed. A support offering which may be more appropriate for some customers is telephone support. This service is often most useful for people seeking assistance but also could encompass bug-fixing, at least for some kinds of bugs. Classes may be located at the customer's site or the training company's site.
Classes typically have a standard curriculum.
Another well established business, although not necessarily in a specifically free software context, is hourly consulting or customization. The customer will have the consultant come in, look at the customer's use of the software, and offer advice, help set up the software in a way that matches the customer's needs, or write software to meet a specific need. The most common arrangement is that the customer receives ownership of any software produced. Providing for the software to become free software instead would change the business arrangement relatively little in many cases. One is internal code cleanups.