Here's my 'bug check' notes;
Google images of lice/mites and their eggs before the inspection so you'll know what you're looking for.
Part the feathers right down to the skin around vent, head/neck and under wings.
Best done well after dark with a strong flashlight/headlight, easier to...
Could do fecals for worm loads.
Definitely examine closely for external parasites.
Otherwise just observation for other issues.
You've probably seen this before, but;
BYC Medical Quarantine Article