Liber Usualis

so I think that I was offered a Liber Usualis today. But I'm not quite sure. And I definitely turned it down (regretfully...)
I was in a someone's office, and I noticed and said, "Hey! You have a Liber Usualis!" (on the bookshelf.) And he was like, "Yeah, do you want it?" and pulled it off the shelf.
My first thought was, "of course I want it!"
but my second thought was, "How do I know if he's offering to give it to me or just letting me borrow it or just showing it to me?"
my thinking is never very clear in these situations requiring great amounts of immediate tact (which I lack in general) in a very short amount of time.
How I wish I had said, "To borrow?" or something like that to which he easily could have replied, "of course," or, "oh no, to keep!"
But I figured in that split second that a Liber Usualis is far too expensive to be giving away to people that you don't even know all that well, so I decided that he meant to borrow. so I said something like, "Oh no thanks, the library (at school) has copies I can check out anytime..."
sigh. hindsight is always 20/20.
why am I not a more articulate person? Or someone who always knows what to say to prevent situations from being awkward?