Arsthbt

There are seconds during this week/month/year that you will not trust me a bit. --Bob

There are ways to manipulate this in his favor, such as stating the opposite of what he wants in the simplest way possible, but because as little as possible is changed, this can be tricky in some cases since only one detail of his statement must be false in order to render the entire statement technically false.

Bob wants actually to state things not as simply as possible, since as you mentioned, this leads to several possible outcomes. He wants to state things as precise as possible.

"My net worth is at most 10 dollars", has the logical (and only possible) opposite "My net worth is more than 10 dollars" (and Bob will have net worth of 10.01 dollars if taking the path least resistance).

"The set of people who distrusts me is non empty" has opposite "The set of people who distrusts me is empty", i.e. no one distrusts Bob...

You kind of answered your own question, he can't remove this superpower by stating he has it so he can go up to anyone, explain the way the power works and then demonstrate it using some easy cases. People will be skeptical at first but will believe him after enough convincing examples.

NOTE: This answer assumes Bob cannot make people trust him simply by saying "You don't trust me".

It's very easy to get people to trust him. Simply announce in a loud voice the opposite of what you want and soon people will pick up that the opposite will happen. If you want people to notice faster do it in a casino.

It will take some time to fine-tune what to say, but this is essentially a wish granting power. You just have to phrase it a little weird.

Your friends will all want you to say things like

My company's value will go down

Or

It'll land on black

Or

Your marriage won't last

Several economic indicators are like this. Things like more stocks being issued (IPOs) and more credit being available happens before a stock market crash. People watch these and try to time the market (but rarely succeed).

The real curse is to say the truth but have no one believe you like Cassandra

It is really simple.

Don't try to make them believe you. Always tell the lie that they won't believe to get them to realize the truth.

If your friend asks if you want to head out to dinner and you do, actually want to, say "no." Your friend will know that you can't tell the truth and know what you are saying.

Once enough people know about the power, everyone will know that he has to speak that way.

Also, he would be in high demand for anything that requires safety.

Any time he gets on an airplane, all he has to say is "this plane will not land safely."

He can be the benevolent doomsayer.

In @KaspervandenBerg 's answer:

There are seconds during this week/month/year that you will not trust me a bit. --Bob

due to least resistance, you end up with people only trusting bob slightly more than a bit.

I propose this:

You trust me less than you trust everyone else.

Bob can be a superhero and become rich really easy.

All he needs to do is to spread conspiracy theories.

Bob says the Earth is flat. The Earth assumes a spherical geometry. Had Bob not used his power, we would eventually be suffocated by the giant elephants' magical freezing farts which keep the frozen barrier st the rim in place, or we would eventually be smashed by the cosmic turtle's sexual partner.

Bob says aliens are abducting people and probing their cavities. Now the aliens can't do that - Bob is a one man X-com!

Bob says planes leave out chemtrails that are used for mind control. Now they don't anymore! Take that, Illuminatti!

And so on. The only conspiracy theories he can't defeat are vaccine and GMO related ones, because those can actually cause direct harm to people.

So most everyone from the average Joe to the eggheads of our time will not trust Bob, but that's not a problem. He will have the undisputed and unwavering trust and loyalty of basically every Infowars follower. He can even take over Alex Jones's place and make huge loads of cash that way.

Heck, Bob could even easily become the next republican president, and he would save the world from climate change by claiming that coal is cleaner than solar and wind power.

How linguistically savvy is this superpower? How linguistically savvy is Bob?

I'm assuming here that Bob wants to communicate the truth and wants to be trusted. I'm also going to be treating the superpower as an antagonist to this goal.

If the superpower can recognize the intent of his statements and will change the truth of the part he intends to communicate, he's kind of stuck (although maria_c's answer is a good one for getting as close as possible to the truth).

If, however, the superpower only analyzes his statements in terms of syntax and semantics, Bob can work around the limitation in various ways.

First, he can use questions instead of statements. While declarative sentences have a truth value (as long as they aren't paradoxes), interrogative sentences do not. So if he wanted to tell you that Madrid is the capital of Spain, he could ask you "Did you know that Madrid is the capital of Spain?"

Second, he could always tell you what he wants you to know in a content clause. This will still involve a declarative sentence, but by selecting the main clause carefully he can make a sentence that is false (and therefore exempt from the power) with a true content clause ("No one knows that Madrid is the capital of Spain.").

Simple, there's a class of people that do similar all the time: Be a denialist speaker.

Many people will believe what's most convenient if it's said with authority and minimal requirement for thinking or action on their part. Just look at flat earthers, climate deniers, anti-vaxxers, and similar.

Just support wrong things with momentum, and everything suppporting that wrong thing will believe him.

Couldn't Bob simply tell someone he meets like some girl he likes very much and after many different machinations and presumed falsehoods he'd say something like "You simply do not understand me" by accident? In that way someone actually WOULD understand Bob's superpower without being harmed? Then communication could be carried out albeit in a very curiously and perhaps very humorous way. Just a thought.

It would be interesting to have a scene of an argument between Joe and Bob perhaps... I don't know how you'd do it but it could amount to a superpower Abbot and Costello routine.