I think in a perfect world the motives would be clear and there would be no reason to question yourself. I also believe in honest communication instead of just playing the cat & mouse game or whatever you want to call it, I think it's very immature of people to do that.
The reason why I'm saying that I'm not sure is because, in the past, I've experienced things that really made want to question the persons character.
Here's one of the two stories :
One of my co-workers was really flirting with me back then, she was winking at me, touching at the shoulders from time to time, also making long talks during our break and talking about this and that, which of course would automatically will make you think that "hey she IS interested in me", but as time went on, I came to find out, her motive was 2 fold, she was trying to get me on her side because she knew that I had it good with the other girl, whom she did not like. So basically she was just trying to get me on her Team, in order to get her fired. But of course I saw that and did not play that game, which made her go mad because I figured out her whole game and I saw her for she was, a proper backstabber.
Lesson Learned Here : Girls like these would do anything it takes to achieve their goals, they plan on playing dirty, they are going to shower you with compliments, they are gonna flirt....till they get their goal.
Here's the second story:
At a bus station, a girl was always getting near to me, touching me on my shoulders, joking around, getting to know me more and more, was very frequent with the touches, as a third person seeing, you are able to say "hey, she IS flirting with you", I am not saying she was touching me sexually, but the indication of her interest was pretty high, I asked if she has plans for the weekend and if we should do something together and she said "she was busy", which was more than enough to me to know, that she only likes the attention but I gave her another chance and after 2 weeks asked her again and she said "oh my schedule is really busy for the next 3 weeks", I ask myself, if I was interested in someone, even though I was busy I would still let them know about when I'm free to schedule something together, but since she didn't, it was clear she was not interested.
The Lesson Here Was : Some girls just like to flirt, they want the attention, they want you to like them, when you give in that you are interested, thats all they wanted to have, their Ego's being stroked, these are also the girls who are like "I am very touchy feely, my family is touchy feely, I express myself like that, it's normal, I am friendly with everyone, you guys just don't know when we are being nice and take it as we are interested".
So that brings me to my current situation, in my experience if you are not sure about something or you have to ask someone (which i just did), the chances are something isn't right, either you wait it out and let the time clarify everything or you go out with your gut and say "I'm still gonna take a chance".
I am personally not gonna do anything and just keep it neutral, because I am at the point, where I hate questioning myself, because the chances are if I am questioning it, the chances are, the messages I'm receiving are very conflicted as well that makes me go on that unknown rollercoaster and by knowing myself, I eject myself pretty early in these situations.
It's just very sad to see the state of girls these days, of course not every girl is like that, there are good ones there as well, but seriously where are they, I see the same thing over and over and over again, girls cheating, losing interest, finding someone new (which was mentioned in this thread as branch swinging), no wonder cheating and the rate of divorce is high these days.