Is rate or consistency of flow related to quality when pulling a shot? Depending on the many variables applied when pulling a shot of espresso, the rate and consistency of the flow of the espresso varies.

Does variable speed or consistency suggest that a shot will be of lower quality? Conversely, does a steady speed and flow indicate that a shot will be of higher quality?
A more watery/lighter consistency with a high flow rate is going to leave you with a terrible tasting shot of espresso with too light of crema (this foam on top can tell you a lot about a pulled shot even if it does look as if it came out OK). The opposite applies here to, a super dark and slow pouring shot can occur too.

In my 4 years of coffee house experience using professional grade equipment it all came down to the grind size. You can tell just by the way the shot pours out. If it's quick make the grind a little finer, if it's slow make it a bit more coarse. 

And also depending on the temperature in the room can effect the pulls as well, half way through my morning shifts I would have to adjust the grind.