Fiber internet is an interesting one - where the incumbents will "dump" (not necessarily below cost, though who knows, but below market rate) if they think you intend to compete with them.

HN is filled with stories of exorbitant rates from AT&T and Comcast that get slashed 70%+, speeds doubled, as soon as a newcomer is ready to offer fiber.

In fact, there was even a story here of a community where they formed a company that could not have done it, or not without a huge effort, but just hinted that they were exploring offering fiber to a town - and just that hint was enough for Comcast to say "wait, wait, we did the math and you all have been overpaying for internet!"