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he's looking to see if the defensive alignment is stacked against the play called in the huddle. 

He may have the latitude to audible to a different run play or a pass play if the defense is crowding the center of the line and an inside run is the play

Otherwise he's checking LBs and safeties to guess what coverage they are playing - zone or man

also now with the proliferation of the RPO, the quarterback might call the play at the line and it is both a run and a pass, with a quarterback making the Quick decision based on the movements of one particular defensive player, most often a linebacker or defensive end.

this is most effective when the defense shows a disguise and then shifts the Dline to another gap, or the linebackers show run defense and then drop back just before the snap

same goes for the safeties moving at the snap

As I really don't know much about "inside football", I thought maybe some of youse guys could enlighten me, and perhaps others.

Here is my first question, it's first and ten from your own 25, the QB comes up to the line and surveys the defense, what's he looking for specifically?  Presume said defense is of a standard type.

Here is a straightforward, short video that illustrates basic and a few advanced
https://m.youtube.com/watch?v=v_61y2yr_9g

The answer to your question is different at different levels, as has already been said.

At the high school level, the QB (if the HC trusts him to) is probably limited to about 3 pre-snap things:
1 - ID the MLB (to see if the defense is balanced)
If the defense is unbalanced and a run to the crowded side is called, he might do a simple audible.  Say it's a run to the right and the safety creeps way up on that half of the field, he'd yell something like "check - Lucy" which flips the same play to the left.  He'd say any word starting with L. 
2 - Is the coverage man or zone (pre-determining if he may be throwing more to a spot or area vs leading his receiver(s) with tight coverage)
Again, for high school, a man in motion gives it away, but so could positioning.  If a safety is walking up and aligning himself with a slot receiver, that man suggest man.  If both safeties are ready to backpedal at the snap, they're probably in a cover 2 zone. 
3 - generally looking for an obvious blitz - if he can tell where they're coming from, then he can automatically throw to the vacated space - a quick dump off to the TE if the LB who would be covering him or that zone threatens blitz.
.
If a QB can do all that with some consistency in HS, he's good and if he can do any more than that, he's probably a name guy on recruiting rankings.  I doubt many of the super-athletic guys can do all 3 consistency (because they don't have to, in order to be successful).

Do they tolerate mediocrity?

I mentioned before that the defensive alignment, to me, very often looks very standard, and yet the QB sees something, or perhaps he's noting it's standard and calls out an assignment (as does the center).  Let's say the play called is a short pass to the TE on a crossing pattern.  It's the first play of the game.  The D is not in any special alignment, they are where they often are.  Is there anything that would cause the QB to audible or point or anything?

Yes.  If you watch that short video I included above ( and it has nothing to do with Florida State), there are several things that could cause concern.
if the defense brings a safety up to man press coverage on the tight end, it will be difficult for the tight end to get open on a crossing pattern in the proper timing if he is jammed at the line by a good safety.  However this will create an opening in the seam on which ever side the tight end he is targeting is lined up on.  The quarterback may audible to a corner covered receiver to drag route into that scene since the safety has been pulled across the middle trying to follow the tight end.

In today’s modern off fence to quarterback would just read that and keep the same play because that drag route is already being run and will be open anyway if the tight end is not open

https://matchquarters.com/2016/08/22/tight-end-sets-vs-match-quarters/


A good read on the chess match that is todays attempts to defend spread or pro spread offenses.