The Bible doesn't make a point blank statement to describe the people easiest in the world to fool -- "they are. . . ." You can cull this information from a cumulative view of all of scripture though. On top of that, it has been my observation.
The phrase, "a sucker is born every minute," is associated with P. T. Barnum, the circus master. The origination of the statement identifies with gambling and con men, saying, "There's a mark born every minute." "Con" means "confidence man." Researchers into confidence tricks defined them as "a distinctive species of fraudulent conduct. . . . intending to further voluntary exchanges that are not mutually beneficial." The purveyor of the trick became also known as a "con artist." Those fooled are labeled by the cons: marks, suckers, stooges, rubes, or gulls (the latter short for "gullible"). The people of our church know that very often, I say, "people think they're getting something, but all they're getting, is getting gotten."
The one quality that I see today of those easiest in the world to fool is "niceness." Niceness is the most important trait to fooling them. They latch on to those who are nice to them. The marks or stooges themselves aren't nice -- usually not -- but they are suckers for niceness. If you brag them up, promote them, say nice things to them, tell them how great they are or look, they will usually trust you, that is, you'll gain their confidence. If you are not nice to them, that being the one redeeming trait, they reject you. Just be nice to them. Never say an unkind word to them. Put heart and like on every post and a nice comment, and you've got yourself at least a superficial supporter.
This "niceness" is a chief replacement for biblical love. Actual love isn't a con. It truly does care about what is best and most important for a person. Love isn't fooling anyone. It tells the truth. When I say truth, I mean, what scripture or God says about whatever subject it is. Love says and does what is best for another person, which also includes reproof and rebuke. Those aren't nice.
In Genesis 3, look how nice Satan was to Eve. See how Satan framed God, that God wasn't being nice to her. Satan was nice. God wasn't nice. Eve went with nice. The following chapter, God wasn't nice to Cain. He didn't just accept his offering. On the other hand, He was nice to Abel, which was grounds for Cain murdering his brother.
I like the dictionary definition of "nice," because it does fit what I'm talking about. "Nice" means pleasant and agreeable. The example given in a sentence in the dictionary for "niceness" was also appropriate: "Her sheer niceness won her many friends."
Of all those prey to niceness, women are the most, and especially young women. This is why 2 Timothy 3:6 says, "they. . . . lead captive silly women laden with sins, led away with divers lusts." It is why younger women in the church need to submit to older or more mature women. Con men themselves say that young women are the easiest marks, especially under the influence of a little bit older man. If you have a young woman about 16-25, she is most easily conned by a man 20 to 30. He does this by saying and doing nice things to and for her. This is how young women give away their purity and virginity. They also stop listening to their parents.
I'm not saying, don't be nice to people. We all should be nice whenever we can. It's not that important though. Being nice all the time is not only not required, but it's required not to be nice in many cases. You can't love someone and be nice all the time.
Niceness becomes the currency of societal acceptance. It is a requirement on social media. You can accumulate numbers of friends on social media by using your niceness currency. Someone uses the Lord's name in vain. Be nice. Someone uses a foul word. Be nice. Someone lies. Be nice. Someone shows up naked. Be nice. Boy comes out as a girl. Be nice. Two men kissing. Be nice. You'll get along with all of them, and they "like you." You recognize that you've got keep being nice. That's all it takes. As society crumbles around you, taking that steep slide toward Sodom and Gomorrah, you just keep being nice. Everybody gets along with this singular ethic of being nice.
If you aren't nice, you won't be treated nice. You know that. A whole theology can develop around niceness until every interpretation of scripture submits to niceness. Every point of view you take relates itself to niceness. It's acceptable belief and practice if it conforms to niceness.
Does God want you to be nice to everyone on every occasion? No. What I've witnessed is that people won't be nice, when you're not nice. This is the point, I believe, of Proverbs 18:24, which in the King James Version reads:
A man that hath friends must shew himself friendly: and there is a friend that sticketh closer than a brother.
I grew up thinking that this was a positive first statement. It's good to be friendly, because you'll have friends then. Being friendly is almost identical to "be nice." If you want to have a lot of friends, just be be nice. It isn't positive; it is negative. The friendliness of which it speaks is a type of perversion, because it is pandering to people. You aren't causing necessary division, required by God in scripture, by not being nice to people who don't believe right or do right.
The second half of Proverbs 18:24 relates to the first. A true friend doesn't demand friendliness. He's going to be loyal. Keeping friends by being nice to them is a recipe for disaster. You'll have a group of sycophants like one sees on social media among millennials (yes, I said that word again). Psalm 101:3-5 provide a contrast:
I hate the work of them that turn aside; it shall not cleave to me. A froward heart shall depart from me: I will not know a wicked person. Whoso privily slandereth his neighbour, him will I cut off: him that hath an high look and a proud heart will not I suffer.
This is David saying, I'm not going to be nice to people. If you keep being nice to people, who are living in sin without repentance, you will get more sinful living. You don't want that. This is why 2 Thessalonians 3:14 says:
And if any man obey not our word by this epistle, note that man, and have no company with him, that he may be ashamed.
You see the same type of treatment in 2 John 1;10-11 in a different situation:
If there come any unto you, and bring not this doctrine, receive him not into your house, neither bid him God speed: For he that biddeth him God speed is partaker of his evil deeds.
Those being fooled by niceness, because they've reduced their standards to niceness mainly to them, see most everything through this lens of niceness. They've stopped being discerning, as scripture calls upon them to be, except in the one area. They know when someone isn't treating them nice. So what does the con man do, any type of deceptive person do? He treats them nicely and he knows he's got them. Whatever they want to do gets approval, except for the lone standard of niceness.
What do you hear as a common judgment of someone today? "He's a really nice guy." "That's good!" "She's so nice!" "I've got to get to know her." People have become so accustomed to this as the one vital trait, niceness, that they adjust their lives to it.
Some people think I'm a nice guy. Others think I'm not a nice guy. I try to be nice as much as I can. If everything is reduced to nice or not nice, I believe I'm less nice than ever. We need men who will stop being nice, and take their model as the Lord Jesus Christ. It's easy to say that Jesus was hated in His time on earth, because He wasn't nice.
Those who mandate niceness aren't nice if you aren't nice. I've found them to be some of the meanest, most disrespectful people I've ever met or seen. They hate people who are not nice to them. Hate them. They treat them with hatred. They treat them in the most vile, hateful manner that anyone could treat anyone. All it takes to not experience this hatred is to be nice to them all the time. It seems simple doesn't it? Even if they don't really believe in niceness. They just want it all the time for themselves. They'll hate you if you don't. They'll ghost you if you don't.
Satan is a liar and the father of it (John 8:44). The effectiveness of his lies, as seen from the very beginning, relate to how nice he is. He's lying, but he's a very nice liar. He keeps people under the deceit of his lies by the niceness of them. Everything will keep being nice for people all the way into Hell.
The easiest people in the world to fool are those for whom niceness has become the overriding condition or standard of their lives. That's a lot of people today.