Surety bonds may be useful when you need the services of someone whose reputation is unknown to you. Three parties are involved, the writer of the bond, the bonded and someone who contracts for the service and may be damaged by failure of the bonded to perform. A bond may protect the service buyer against failure of the service seller. The bonded pays the bonder and receives a bond which can be displayed to the service purchaser. The purchaser has recourse then to the bonder in case of default by the bonded. Here(?) is one collection of information about how they work.

One can easily establish a pseudonym and furnish it with a public key. If the corresponding secret key is used with care the reputation of the public key can be protected Bootstrapping the reputation of a public key should be difficult, however.

A bondsman for pseudonyms might accept anonymous payments accompanied with a public key. The bondsman would hold the money and publish a bond; to whom it may concern. The bondsman would be thus commissioned to judge conformance to digitally signed contracts. The bondsman would be judge and jury and make decisions for a cost of perhaps 10% of the bond.

The bondsman would have a reputation to protect with both classes of customers—the bonded and the service buyers.

I can imagine a bond for as little as $50. The bondsman would be required to make a snap judgment in case of conflict. Repeat business with both the bonded and the buyer would be required to make this economical.