Just a reality check:
I must say that car mechanics I come across are mostly rogues.
and
I must tell that car mechanics I come across are mostly rogues.
Would the second sentence sound unnatural to a native speaker? Would it be different in meaning or tone?
I know that we usually use an object ("tell you") with tell but still, would it be passable as a stand-in for say in this case?
If it would indeed sound strange, would this introduction of an object suffice:
I must tell you that car mechanics I come across are mostly rogues.
Would this be fully analogous to sentence 1?
Best Answer
The second sentence does sound unnatural. "Tell" needs an object in this case.
The first and third sentences both work, and mean almost the same thing. The third sentence focuses on telling you something. Out of context, it sounds more like a direct warning -- "Hey, pay attention to this, car mechanics are trouble!" The first sentence sounds more like a remark or opinion -- "Speaking of car mechanics, I've met a lot of dishonest ones." It might be agreeing or disagreeing with another sentence. These are only small differences, though.
Also, you might want to put a "the" before "car mechanics". It makes the sentence sound smoother since you're talking about specific car mechanics (the ones you come across).