The opening question is under the assumption that high amounts of crime do occur. On land that does have a notable probability of crime, simple insurance business will not be capable of providing sufficient compensation, and may bankrupt themselves if they do not hire a protective force. I do not think such high crime areas are likely in a free system, but assuming they exist, this is a solid solution to the alternative.
No one would be required to enter areas managed by such businesses. But, for the people who do they could enter with confidence that competition and reputation maintenance would keep such businesses from framing them for crimes, or committing other wrong acts against them. Insurance alone would give people more reason to do nothing to stop theft, and would encourage staged activities to obtain payout.