Indirect methods to find out whether he/she is single

Pay attention to body language. Note that the way this person interacts with others can also help you determine if he or she is willing to engage in one night hookup. If this person is with another person or a group of people, then pay attention to how he or she interacts with them. Try to glance at this person from time to time to see his or her behavior, and this is important for yout inder hookup.

For example, is this person smiling close to someone? Is this person holding hands or touching someone else's arm or back? These things may indicate their relationship status. People are not single. However, if the person does not show any intimate body language, then he or she is likely to be single for one night hookup.

Check the ring. A wedding ring or engagement ring is a solid evidence of a person is available or not. If you are close enough to see this person, look for a ring on his left hand. People usually wear a wedding ring or an engagement ring on the ring finger. If there is no ring, then this person is likely to be single. However, keep in mind that many people have a stable relationship without getting married and a wedding ring.

Introduce yourself. If you have reason to believe that this person is single, then you can introduce yourself and start to get to know the people you like. This time you are going to need more solid proof to find out if he/she is single or not. If the person you are interested in is in a large group, you can introduce yourself like this "Hey, I’m Richard. How do people here know each other?"

Learn about this person. When you first meet someone, it is good to ask some questions to better understand this person. Giving the other person a chance to talk can also reveal whether he or she is dating someone or not. Some good questions include:
Where did you grow up?
Where do you work? Do you like it?
Do you have a pet?
What do you like to do after your work?

Ask about their weekend plan. If this person is not single, then he or she is likely to have a date with their significant other on the weekend. Feel free to ask each other's weekend plan, which may give you an answer to your question and a good opportunity to ask for a date. You can ask “What is your plan for this weekend?" If the other person says nothing, you can try to say “there is a new restaurant open on Saturday. Do you care to join me?”

If this person says that he or she has a date with an important person, keep calm. Try saying "Great! Have fun!" It may mean that he/she has a lover, but if they don’t. You can ask them out again for some other time. If you are rejected again, it definitely means that either they have someone already or they are not interested in you.