I agree that most book's would be very limited in the info you could obsorb, An inspection should only take a few moments and handling the roo properly is critical to a good inspection. here are a few things I always check for when inspecting a bird for any reason.
Hold the bird with one hand under him and the other free to work with.
Hold the birds head close very close and smell the head, ears, nostrils and breath. You are smelling for an off odor that may signal an infection of any sort, looking into the eyes for clarity and sign's of discharge. Listen to it's breathing for sign's of labored or a gurggling raspy sound, sign's of CRD.
Inspect the vent. Pull the feathers away and check for lice and mites, inspect for a healthy vent it should be moist and plasid and med pink in color. Milk it for an idea of the quality of his sample this is very critical.
Look under the wings close to it's body for any other sign's of pest's and any off coloerd feathers that will hide there as a sign of his true feather color.
Locate the crop feel it and move it around sqeezing it to make sure it moves freely and isn't impacted.
Inspect the feet and leg's. look at the bottoms for sign's of bumble foot or previous bumble foot, Inspect the spurs and see if they are long enough to twist off for protecting your hen's. Inspect the leg scales, if they are lifting off the leg slightly and are dry and can flake off, then there may be scaly leg mites present.
Doing things like this will during a 2 minute inspection will greatly increase your chances having a good experience.
AL