Quote:
parents do this all the time because they think their kids are so special.
It is a salesman's job to be nice. so I agree with you, she was just being nice.
No way for us to know for sure, since we weren't there to see how girl was interacting with OP.
You're right, this happens a lot with parents, but that doesn't necessarily mean it's always true.
OP: always assume interest in a potential lay/attractive woman. Try to always have a sexual mindset around them and go for it. I like 60yoc's simple tool for getting you excited enough to hit on a woman whose interest level you're not sure about: Imagine her face down on your dick, blowing you. Should get you in the right mindset pretty fast if you genuinely have interest in her.
Just be prepared for rejection. Get used to being in a sexual state of mind around every potential mate though, and your success rate will improve. Everyone fails. Embrace it and keep going.