Low mark ups are possible when resources are managed well. Not all "test companies" have repeatable build and assembly processes, time-management discipline, and best project management practices to ensure a test system's variable costs are the most competitive.
Additionally, not all "test companies" consistently apply best practices to evaluate test system performance; and identify how to increase detection coverage, first pass yield, test time, and up-time.
Ask us, what we do and how we do it.