How can u tell if she really has a BF

This girl i approached the day before and made some small talk about movies etc...we defiantly had good rapport and i made her laugh a lot...but due to an interruption i was unable to close...so the next day i approached her and said hi, and she gave me an enthusiastic hey back. then i said.
“hey so I only have a couple of minutes (time constraint) but you seem like you need to get out more (she laughed) so ill do you the favor by taking you to Princeton tomorrow”. She said “oh” disappointedly which first made me think she was busy, however she then told me still sounding disappointed, that she had a boyfriend. It kind of seems like she did because she seemed sincere.
I just left it at that and said see you later. Is there anything i could have done differently, and is there a way of telling if someone really has a boyfriend?

She was enthusiastic about you. Even the next day when you met. So I think she's probably sincere here. If you really want to know when people lie and stuff start reading general body language books.

IT doesnt matter, especialy ona night out. girls only really tell you they have a boyfriend for several reasons. but none should scare you off. because you should be coming across as a friend.

1~ you come on too strong and it scares her-she will lie,say her nice male friends her guy, reveal she has a boyfriend, or just say she has one to get you away. play it, say"erm ok? but i dont see how taht has anything to do with blah blah blah" make ehr feel foolish for saying it like the very idea of you hitting on her is obserd, fromt hat talk abit more and excuse yourself with your time constraint or change targets.

2~shes testing the water, shes trying to see how you react to the idea of her being taken, she may have a bf and is so attracted to you that shes willing to cheat, if so carry on, she may be open to the idea but not sure and wants tos ee how you react to the idea.(remain strong in this case), maybe she hasnt got one at all and she just wants to see if you'll stick around casue your genuin if so keep at it. aslong as you get ioi's you keep sarging and escilating.

3~shes done! look for body language how IOD and then excuse yourself doesnt amtter if she has one or not simply admit defeat at some point you've said something wrong, or made a fool out of her 1 to many times either way you dont stick around, use your time constraint and excuse yourself before she or her non-fake Bf kill you for becoming a creep Ha!

on a side note dont worry about the BF thing, its not your responsability to moderate their relationship if any. and you cant help who you are attracted to. never ask about boyfriends and never care what she says, care how she acts becasue you shouldnt end your game becasue of a b oyfreind that may not exist and miss out on either a girlfriend, a good night(s) or a friend that oculd lead you to other targets!

best of luck

I also think she was being honest. The above comments are excellent. Since most attractive women also have attractive friends, I would get to know her better as a friend, but don't change your behaviour because she obviously is receptive to it the way it is.

Keep in mind that your behaviour will likely be sending mixed signals relative to a comment like "I was looking for a new friend."... which is a good. Keep in mind that people who are direct all the time become predictable which is inherently boring. Boring is bad when trying to create an exciting and interesting experience for a woman (and yourself).

Once you get closer to her, she'll start introducing you to her friends and you can move further from there. And who knows?... she may even leave her boyfriend for you if she feels their relationship is not "good enough."

- Spool

Solid advice. I haven't encountered a situation where a girl has said "no, sorry, i have a boyfriend", so as a sidenote to this I wonder if there are any good, quick retorts to this so that there is not an awkward moment afterwards. I've been thinking of just random sh1t to say like "ohh, wow..i have a cat". I liked Bradders' advice about acting as if it is not a pickup situation. any other ideas?

its also good to act like your gay.
seriously lol, "if i wasnt gay you'd already be mine" works pretty weirdly well! maybe jsut acting gay, they are pleasently surprised when you tell themy our not. if you've spenjt the lst 20minutes with them and them loveing you and being fien around you casue tehy think your gay, only for you to remidn them subtly your not. suddenly they dont know how to act, then wheny ou act interested again they are already comfortable with it becasue you wer ejust doing it before and tehy were fine becasue tehy thought you were fay.
catch 22

best of luck