You're usually the initiator.
Are you the “initiator?" You know, the person who is almost always the first one to call, the first one to text. Unless you’re some crazy, obsessed person texting and calling them every 10 minutes, then this is a clear red flag that the feelings are not mutual and that you’re just an option to them.
They Lie About What They Did or Have Vague Answers
If you ask them what they did this past weekend or some specific day, they say something like, “Oh, just chilled,” or, “Went out for a bit, kinda boring.” yet if you look at their Instagram or Facebook, it tells a completely different story. They tell you this because they don't want to bother explaining to you what they did, especially because they know it's going to lead to more questions. They see no point in it because they see you as insignificant. “I’m too lazy to tell him/her everything that went on.”
They Flake on Plans
If they often cancel plans on you with poor excuses, it is because something better came up. Hell, if they find you very boring, staying home and watching Netflix sounds better to them. A good indicator that they're not interested in anything with you is when you get the “I’m bored” text. When they want to plan something last minute just because they don't feel like being home alone and want some attention.
They Don't Care What They Look Like in Front of You
They don't take the time to get dressed up or even put on makeup (if it's a female) when they see you. Someone who wants to make a good impression on you takes the time to dress up, to at least look presentable. Not doing so, not giving a damn, is a simple way of them saying, “I don’t really care whether you like how I look since nothing serious is ever gonna to happen between us.”
They pop up only when they want or need something from you.
A ride to work or an event? Sex? A loan? If you're hearing from them or seeing them only when they are getting some benefit, that is, you're doing something for them, then that's a clear indicator that they just want you for what you have or can do for them, not for who you are.