A person who either consciously or unconsciously tries to engage you in a fruitless investment of your energy, time, money or attention. These people can be "takers" or simply abject individuals. The truth is that engaging in these types of interactions is an act of free will on our part so each of us can only blame ourselves for getting sucked in once again.
A person who contacts a company and engages in a long dialogue, full of questions and requests, with the proposed intention of buying a product or service. This dialogue can go on for days or several weeks, but the person does not purchase the product or service. A time waster is also someone who keeps saying he will pay tonight but never does.
That guy is a time waster. He's been emailing me for weeks, saying he is going to be our product but never does.