If you look at corporations now, the ones that are transnational are well known to abuse people, although, not their clients, but their workers in less developed countries. They can't do that in countries they make money in due to the same laws, enforced by central authority.
If you look at modern corporations, again, they don't tend to get a lot of backlash for unethical things, like, everybody kind of knows of Nestle using child labor, which is unethical, everybody know of Amazon warehouses where they squeeze everything from their workers by horrible schedules and environment, all in the name of better efficiency and profit. You have Boeing which has taken quite a few reputation blows lately, and even if their shares are dropped, they're still fine, if something, dropping shares make company less interesting for investors, but failing the company, especially for larger ones, takes quite a lot.
And also, the reason why current governments exist is because this is the favorable position. Powerful entities in ancap would have a huge incentive to become states, and it's not that hard to sell to people, as it happens all the time, people vote in charismatic dictators with the promises of security and prosperity, and people actually love the idea of sacrificing some of their freedoms for security.
This is why governments appeared in the first place, people don't like to be in this state of constant struggle and competition that would be everywhere in ancap, they like being taken care of and live peacefully, so it's worth way more than some vague freedoms and even more than like 20-40% of their income. So i also believe that government-like entities will inevitably appear in free market.