1) First of all, questions that answer with YES/NO are out of discussion, as they would just be 50/50 chances of getting YES/NO and 50/50 chances that the answer is good. How do you deal with persons that ask you YES/NO questions?
I generally don't do yes/no. I try to get people to reword. If I do end up doing one, I'll tell you what the card says about the situation, but not yes or no. I think tarot is a little more complex than two options.
2) If someone asks you to do a reading about his/her love life or generally a reading that involves someone else, what do you do?
I will not try to "enter" the mind of a person without their consent, so I don't do third party readings. But I will do readings about something that affects you and involves another person, as long as you are directly involved. I won't do "Does he have a crush on me?" but I will do "What should I do to make our date go as well as possible?"
3) Tarot is a great psychological tool, so how do you deal with persons that believe tarot have mystical forces and are in need of a positive reading? (in example, going through a crisis) (what do you do if the reading is negative?)
I've never actually had that conversation with a querrent. But if a reading is negative, there are ways to soften it without being dishonest. Another thing I do in those is drawing clarifier cards to answer questions like, "What can I do to improve the situation?" or "How can I manage the way this situation makes me feel?"
4) What spreads do you use and what kind of readings do you do? What questions do you answer and what questions you choose to not answer? (regarding a crisis, if a crush loves him/her, etc.)
Sometimes I go on here or online and find spreads for specific topics. Other times I make one up. Sometimes I just pull cards and go intuitively. My favorite spread is Comte de Mellet, which doesn't exactly have positions, but it pairs cards. As for what I won't read, like I said, I won't do third party readings. I also do not answer questions that would be better suited for a doctor, lawyer, therapist, accountant, etc. The most I'll do for those is ask, "What do I need to know about this?" and refer him or her to the appropriate professional.
5) Do you take money for your readings? Especially if you believe they are mere images?
I don't do paid readings yet, but I plan on doing it in the future. I don't think they are "mere images," though. I don't think they're supernatural, but they are complex and meaningful.
6) Why did you choose tarot, even though you don't believe in it having magical forces?
Tarot has always interested me. I was raised religious, though, so I didn't get into it then. I'd been an atheist for a few years before I picked up the cards, and then I did it somewhat on impulse. It was mostly about satisfying that draw I've always had, but once I started doing it, I saw how well it actually works and believe in it.
Also, I wrote this a couple weeks ago about one way tarot might work from an atheist perspective. It's one way of resolving the "magic" part.
http://tarotforum.net/showpost.php?p=4073814&postcount=22
Personally, I'd say try it and see how it works for you. I wouldn't buy a collection of decks or an entire library, but a deck you're drawn to and one good book should help you get the feel for whether it's something you'd like to more seriously pursue. If you don't want to buy a book yet, there's tons of information online that you can use as a starting point. Good luck!