Without a State to enforce contracts, would breaching a contract be risk-free?
Not at all; in fact, it would probably be much more hazardous to breach a contract in anarchy than it is under a State.
Contract enforcement under anarchy
Because in anarchy, although there would be no State to punish such breaches, there would also be no State to authorize them.
In anarchy, everyone would have the option to purchase insurance against contract breaches from competing contract-fulfillment insurance firms, who would investigate claims of breach and compensate their customers if a breach were to be found.
Of course, the cost of such insurance would be proportional to the product of the likelihood of breach and the cost to remediate the breach. Thus, buying insurance against breaches by known crooks would be unaffordable or completely impossible. This of course would not make it impossible to deal with crooks, but only the most careless customers would do so.
This put the burden of determining reliability on specialized firms who would do their utmost to price the risk properly, since it would be very expensive for them to misjudge the risk in either direction.
And to answer the obvious question as to what would happen in the case of an insurance company’s refusal to pay a just claim: that would damage their reputation severely, as anyone who was paying attention would be less likely engage their services in the future.
Who would notify their customers or potential customers of this situation? Their competitors, of course.
Contract enforcement under a State
Of course competition in contract enforcement under a State can also exist, but it is mostly pre-empted by the State courts, which are slow, expensive, and unreliable.
However, in more cases than might be immediately obvious, we can see the effects of social disapprobation acting toward fulfillment of contracts without State intervention.
One example is the “handshake deals” made by diamond dealers in the New York jewelry district. They never sue one another, but they also keep their word as given. The reason, of course, is that anyone who breaches an agreement will be excluded from future dealings with the rest of the closely knit group. This method of contract enforcement would be unaffected in a state of anarchy.
Conclusion
As with other situations, the absence of the State leads to better results than its presence.