Well it's rather rare for me to be complimented especially given how I work at avoiding eye contact and therefore conversation opportunities, so it's more a hypothetical. I'd be skeptical, what did the stranger expect to get out of it? being nice to be nice? not likely.
Yes. At the risk of sounding like the Pit Pollyanna, I interpret compliments from strangers to really be an act of kindness for the sake of kindness. When a stranger has complimented me in the past it really has seemed like a compliment with no strings attached. I say thank you and we both move on. I give compliments to total strangers without expecting to get anything out of it.