Really!? Thai women comes out of nowhere and just tell you that you are handsome. No, they are not! Sorry to burst your bubble, but that it not at all included in a behavioral pattern or cultural ways for a regular, not bar or massage working, Thai woman. I am pretty sure, what we have here is Thai women working in the shops where you buy things. Not like you sit drink a coffee and a Thai girl just shows up, and tell you your are handsome. The ones that tells you this, just wants you to keep on shopping or come back next time.
But, please by all means, approach them with your delusions and try your romantic whip. Just be prepared that they might have a bigger whip and knows how to use it.