I've been burned before, buying entire series before I knew I liked them, which is why I don't anymore -- I ended up reading the first book, and then getting stuck with the other four books of the series which are still sitting on my bookshelf, unread. With giftbooks, unless it's really super expensive, I'd rather give the whole thing. Especially if it's something like a graphic novel, which tends to be shorter than an actual book.

I am more likely to buy a book that ends with "to be continued" if I know the rest of the series is already written, though. Unless it's, like, Harry Potter, which didn't start with TBC endings per se. But, well, Harry Potter is a whole other thing altogether.