What is a typical commission rate for an engineering consultant?

More detail: A friend has been offered a job as a senior level engineer in a very small consulting firm. The vast majority of this engineer’s work will be going to customers and setting up various processes, that is, this is not selling equipment it is designing processes on existing equipment and teaching other engineers how to use the equipment. The company charges an hourly fee for the engineer’s time. She has been offered a small base salary plus a percent of the consulting fees that she earns. There will be some sales but it will mostly be servicing existing customers.

What is percent is standard in this industry?

Haj