When using any of the above six suggested questions, never reveal the true reason to anyone why you are asking them. If an interviewer challenges you to explain the nature of the question, just state the obvious motivation included in each explanation noted above.
This is your question time - they have had their turn. Don't be afraid to take charge of this segment of the interview. If you find that they are compelled to start asking you questions in response to any of yours, provide a very short answer and then move on to your next question. Don't let yourself get bogged down in new questions.
To indicate that you have ended your series of questions, simply say, "Those are all the questions that I have." You might want to glance down at your watch as a subtle hint that you'd like to end the interview. If you think the interview has gone well, then it is in your best interests to end it sooner rather than later. You don't want them to find reasons to change their mind about you.
If you think that the interview has gone badly, you should hope that your questions have re-ignited their interest in you. Don't be too surprised if there is a change in their attitude towards you and they start asking new questions. A very positive sign would be if the questions increase in difficulty. If this then happens you are in with more of a chance than you've had before. If you feel that the overall energy level in the room has increased, then you should work to maintain this increased energy level so as to maintain their new level interest in you. Be even more enthusiastic, more interesting, more dynamic, more friendly and more positive than before you started asking your questions.
Your asking intelligent questions should provide the final confirmation to the interviewers (especially if they already favour you) that you are the person they believe best suit the position. If the interview has gone badly, your questions create for you the opportunity to turn things around. So whatever happens, you won't be the worst candidate that they would encounter and you're more likely to come across as their best option.