How do you know if a person is sincere?

Just hang around with them for a while before committing to anything. You’ll get to know their behaviour very quickly and you will be able to see if they are interested in you or a quickie.
I hope it goes well for you if it works out :) I’m sincere about that.

By their actions.
Do they do what they say they are going to do? That would be a good clue.:)

You don’t really know. Love requires a leap of faith and understanding and I have found in almost all of my relationships you will be blindsided by your S/O at some point in time and you come to realize you simply expected too much. IMO that is why you hear the term love is blind.

Usually, the best way to determine sincerity is to see if actions, over time, match up with words.

They are not sincere if your nostrils flare at the unmistakeable bouquet that puts you in mind of an english meadow on a warm summer’s day….you know, bullshit!!
Otherwise, you’re good to go ;¬}

Yep, it’s the test of time. It can take years to see how people show up under different circumstances, stress, etc.

Someone could be the greatest person ever until a stressor hits and then they could go psycho on you without warning. I always look to see how people show up during stress. It’s easy to be nice and happy when lifes rollin’ along with a song, the true test is in observing how someone handles stress, anger and other less than cheery times in their life.

A sincere and relatively emotionally healthy person may have a moment once in awhile BUT, they will catch it quickly and apologize easily.

Beware of anyone that makes excuses and doesn’t take responsibility for their less than stellar moments.

As others have said, it is one of those things that just takes time. Trust takes a while to build. It is something that can be torn down rather quickly, but even if the trust has never been violated there may be a nagging doubt for a long time.

My girlfriend took a long time to trust me, and then it was just a little bit at a time. And when I was human and screwed up, but immediately apologetic, she talked to me about how it hurt her trust in me. (She has some trust issues to begin with).

I think that trust really has to begin at home, humans have foibles, so, while ‘trust’ is important in our relationships, the most trustworthy trust comes in our trusting ourselves that if someone proves to be untrustworthy, more than once, we trust ourselves to do what’s right for ourselves.

Watch how they treat the waitresses on a date.

@Imadethisupwithnoforethought I laughed XD

Thank you for answering everyone :)

@MilkyWay I am not kidding at all. If they are super nice to you, but kind of a prick to everybody else, assume that they are a prick who is not being sincere with you.

If you want some enlightenment on how a relationship might end up, read the chapter about “John Gottman” in Blink by Malcolm Gladwell. How much a couple looks at one another and acknowledges each other during a 2-minute conversation reveals, as Gottman says, how long the couple will stay together.

Basically, he’s trying to point to how the individuals subconsciously feel about being a couple and how they show that in the little quirks of their personality.

If a couple fits right being together, they are going to show it not in the deliberate displays of affection but in the small things while they are talking to each other. Those small things are what really give away the level of an individual’s involvement in a relationship. So it kind of comes down to the social psychology of the individuals involved in a relationship.

I look ‘em in the eyes and I shake their hand.

…and then I assume they’re not.

Use a polygraph or truth serum.

Swish them with holy water? : )

There are no physical giveaways as far as i know (or someone must be blushing whenever he says something and you never can see a obvious reason why they would be in embarrassment) .
Sincerity might be proven over time, but even then you can’t be sure 100%.
There are examples of spouses who faked feelings and interests for decades, leaving the other half awestruck.

Through actions and words.. If you begin to get a lot of excuses or if their stories seem to vary a lot as in they are lying so much they can’t keep track of what they told you. When a person isn’t sincere they always feel compelled to lie to cover up what they really are not feeling.
Unless they are a sociopath, most people have a problem with looking you straight in the eyes when lying. Also look at their body language. Gestures are a good indicator of sincerity.

From the book ” Safe People” How to find relationships that are good for you and avoid those that aren’t by Dr. Henry Cloud & Dr. John Townsend a brief list of traits of UNSAFE people

1. Unsafe people think they “have it all together” instead of admitting their weaknesses

2. Unsafe people are religious instead of spiritual

3. Unsafe people are defensive instead of open to feedback

4.Unsafe people are self righteous instead of humble

5. Unsafe people only apologize ( or do not ) without changing their behavior

6. Unsafe people avoid working on their problems instead of dealing with them

7. Unsafe people demand trust, instead of earning it

8. Unsafe people believe they are perfect instead of admitting their faults

9. Unsafe people blame others instead of taking responsibility

10. Unsafe people lie instead of telling the truth

11. Unsafe people are stagnant instead of growing

Interpersonal traits of unsafe people

1. Unsafe people avoid closeness instead of connecting

2. Unsafe people are only concerned about “I” instead of “we”

3. Unsafe people resist freedom instead of encouraging it

4. Unsafe people flatter us instead of confronting us

5. Unsafe people condemn us instead of forgiving us

6. Unsafe people stay in parent/child roles instead of relating as equals

7. Unsafe people are unstable over time instead of being consistent

8, Unsafe people are a negative influence on us, instead of a positive one

9. Unsafe people gossip instead of keeping secrets

You don’t really know. Just got to follow your heart!