If a girl isn't doing AT LEAST 60% of the chasing then she isn't worth your time. I think the sweet spot is around 80-20 personally. As soon as she has the upper hand, or shows declining interest, it's time to go complete ghost NC and never look back. It doesn't matter if she's initiated 20 dates in a row. If she flakes on you two times back to back then you kick her to the curb and move on. If she comes back you can decide where to go from there. If she doesn't, you saved yourself a lot of trouble and she was never worth your time anyway.