As I understand you are looking not for an API solution, isn't it?
If so - please move the question to general section
If no - and you like an API solution - you may check the distance between start or end point (SketchLine::GetEndPoint2/SketchLine::GetStartPoint2) of both lines in order to identify whether the line is flipped.
Application Engineer at Intercad
Tel: +61 2 9454 4444