Other painting techniques like ink shading have a lot less individual quality from the beginning. But a careless applied ink or colour shading in a painting of one of the best painters like Tanyuu, Tsunenobu or Ganku is unthinkable. So in this case the general level of quality can tell us a lot too. To obtain the skill of understanding quality of ink shading, a thorough study of references is essential. One has to know how a certain painter usually does it.

When we discuss the individual calligraphic quality we mean of course all the brushwork. The general body of calligraphic strokes in the painting or calligraphic text is the important part.
The small, to the forger well known example of a signature is much less important than longer calligraphic texts or the painted subject.
Even less we should care about the seal imprints. Carved after a model a good forgery is easily achieved. Now even done with modern reproduction techniques so that there is no difference.
And such a imprint of the same seal might look very different anyway. Just take a look to the example of the seal prints on Ganku’s fabulous set of Tiger and Dragon. The seal imprints on the two paintings of one set, do not make a fine set at all.

A fascinating painting with a great quality and a bad seal, is still fascinating and excellently painted!