I live in Germany right now and I want to go to Greece. I am a non-EU citizen. Do they check visas?
There are two sides to this, the airline and the authorities.
On the airline side AIUI Ryanair demand a "travel document check" but most other airlines do not. It is not clear how in depth this check is.
On the immigation authorities side there are not supposed to be long term systematic checks but AIUI there can be random checks, intelligence driven checks and temporary systematic checks.
When it comes to actual border control, none is performed going from Germany to Greece.
Coming back, however, Germany currently are performing checks on passengers arriving from Greece. I called the Bundespolizei in Munich, who said that flights arriving from Greece park in the non-Schengen sector of the airport.
In this case, make sure to tell the police you're arriving from Greece so as not to get a second entry stamp (as you never left Schengen to begin with)