Based on the narrow case of a business relationship that consists of just one transaction, I don't think there is a single word answer. In the single transaction, buyer and seller would rely on verification, not trust. In other words, the buyer would inspect the product carefully (or have a trusted independent inspector evaluate it), and the seller would either demand cash or have a trusted independent authority (bank, etc.) verify that the buyer's means of payment (credit card, check, etc.) was legitimate.
However, in the case of a recurring business relationship, verifying every transaction might be inconvenient. For example, if I sell you a truck load of apples every week, it costs a lot of time for you to inspect each apple, and costs me time to make sure your check is good. In this case of recurring business, @ermanen is correct: "interdependent" is the right word.