Approachable?

I don't know if I should be flattered or slightly offended that a married couple would approach me and ask me to be apart of their threesome. I mean on the one hand, i would be totally down and I am flattered that they think I am hot. Then again on the other hand, kind of awkward to come into a relationship and openly be the other woman for both of them, while also taking into account that i could possibly look like I am just DTF (down to fuck). I would think nothing of it if this happened to me only once, but this has happened several different times mainly while I was at school in Hawaii, and a couple times when I was home in California. I've never accepted mainly because its awkward, and I would much rather not be in that whole mix if something were to happen out of the norm.