Well, some well-reasoned and logical responses.
In the first instance, you're right, communication does indeed pose a problem, and does even now. However, in the market, when one party is injured, it's not just them that stop dealing with the inuring party. Word of mouth is a pretty powerful force, especially in a small community. The world is getting smaller, and information only has to go through 5 or six hops to get all the way around the world.
Information can spread very quickly, yes - the trouble is that it's not necessarily
accurate or
truthful information. Have you ever heard the saying "A lie can travel halfway around the world while the truth is still putting on its shoes"? In order for this to work the way you'd hope, each person would have to have the ability and time to personally verify the information they receive - and even that might not be enough due to social pressure to ignore contradictory facts. Worse still, if someone owns a significant chunk of the media they can and do direct this social pressure.
Imagine what it would be like in an even more connected world. Piss off the wrong people, and you're penniless.
That's the problem with your idea. It's not doing something
immoral that leads to you being penniless, it's crossing the
wrong person. Could be that you kicked up too much of a fuss about them scamming you or robbing you or raping you or beating you up. So long as the influential evildoers stick to doing it to people with much less social influence then themselves, they can essentially get away with it - crossing them carries too much risk and those with the influence to damage them have no incentive to do so.
In the second one, What you've described is essentially the enforcement mechanism in an AnCap society. Unemployment would only come to those with truly nothing to offer, and for those few unfortunates, charities, or more likely employers who are willing to train, would take care of them. Shunning, excluding someone from interactions, would only come as a result of failing to enter arbitration. So while death by starvation is possible, it's not likely to come from simple unemployment.
That would require the way people think to change in ways that, frankly, are probably never going to happen. Currently whether someone's seen as having "nothing to offer" is determined by extraneous factors like skin colour, gender, class markers, etc, and while attempts to get some of these factors ignored have met with limited sucess no-one's managed to shake off this kind of thinking.