Do you dare to search for pressure cooker now?

Limited yes. That is sufficient example to show that your claim that there is NO right to a private conversation is wrong on its face.

In a criminal case, you might not appreciate the result. The rights in the fourth amendment apply only to the government. As long as the police don't solicit infringement, the courts won't apply the exclusionary rule to keep information obtained by non state actors out of your trial. In some cases you can sue, but you probably could not sue someone who overheard you without using some kind of artificial assistance.

You are wrong about the issue of fraud, and there are plenty of examples of prosecution for entering a property under false pretenses. One famous example is Food Lion vs ABC. Food Lion successfully sued ABC for trespassing when reporters lied to get jobs so they could report on company practices from the inside.A policeman undercover is actually a special circumstance; it is accepted practice for police to lie if it is in the furthering of their duties.