I agree with the OP. You can pretty much judge where you stand with a woman if you keep your eyes and ears open and pay attention to what is going on. This gets easier with experience.
Things go sideways when men engage in magical thinking, letting emotions get in the way of objective evaluation. This causes men to ignore bad signals, while placing too much emphasis on behavior that reinforces what they want to believe.
Two things to remember:
(1) Bad news does not get better with time. It is better to let things end as soon as possible than to drag out a situation that will turn into a nightmare. This reminds me of the old story of the Little Dutch Boy with his finger in the dike. I never understood this story... Why is he sacrificing his life holding back the collapse of the dike... he should have walked away. If you are sacrificing your life and getting nothing in return, you are little more than a useful tool. I know dozens of men that bust their asses keeping things going with particular women... getting little or nothing in return.
(2) "You can ignore reality, but you cannot ignore the consequences of ignoring reality." This is Objectivism, acknowledging circumstance is a key to your mental health and can provide an effective guide for individual ethics.