Based on what hidden and/or publicly available criteria are Schengen visas granted?

score:5

Actually you can appeal a refusal. The process will be described in the notice. That being said, the main criteria are:

Did the applicant read, understand, and follow the instructions? Is the application complete and consistent? Quite a lot of people don't do that ...
Does the applicant appear to be a genuine tourist or business traveller? Does the proposed itinerary make sense? Does the applicant have a realistic appreciation of the cost of living in the Schengen area?
Does the applicant appear to be an illegal immigrant? A steady, well-paid job at home is a big plus. If the money for the trip is borrowed, it might look like an "investment" that will be repaid by working illegally in the Schengen area. Unexplained deposits of money are a very bad sign.
Is the applicant known as security risk? Governments have secret databases. Some governments share some data with others. Applicants who are listed as dangerous (but not dangerous enough to draw a drone strike) would be denied entry.
Is there a known travel history for the applicant, good or bad? Every time a tourist visa was used without overstay, that is a good sign.
Did applicants with a similar background have many immigration problems in the past? That's never the only reason for rejection, but application from some regions are scrutinized more closely than others.

o.m. 34673

Source: stackoverflow.com