Troubleshooting is the work that separates electricians. A dead outlet can be a failed device, a back-stabbed connection that has loosened, a tripped GFCI three rooms away, a loose neutral in the panel, or a utility side fault. Each of those has a different fix and a very different cost.
We test rather than swap. That means measuring under load, checking voltage drop across suspect connections, and reading the neutral to ground relationship at the panel before anything gets replaced. Flickering across multiple circuits at once, for example, usually points to a service neutral problem rather than anything inside the house, and replacing fixtures would have been money spent on the wrong thing.
Most residential diagnostics resolve within the first visit. If the fault is intermittent and will not present, we say so rather than guessing at a repair.
Technician insight
Flickering on every circuit at once is a service neutral problem until proven otherwise, and it is a utility conversation, not a fixture conversation.