what would make you think someone is taken?

I assume someone is taken if they're constantly texting someone, so far it has proven to be true

I used to assume everyone is available until I was told otherwise

If they have photos of the same recurring person on their social media page(s), if they smile or seem a little TOO into text messages on their phone, if they tell you--I can't think of much else at this age.

when u ask dem and dey say yes i yam

When they tell me they are taken or someone that knows them tells me they are taken

When they say that they are.

I tend to start with that assumption.