The document discusses the costs of selling data. Strictly, if data are directly viewable, people can legally copy and reuse them without providing feedback or citations. Encrypting the data prevents feedback. Alternatively, asking everyone to sign agreements or mixing data with creative content could address these issues but be difficult. More relaxed options include licensing costs, but the marginal cost of publishing is low while individual licensing costs are high, and it creates incentives for others to redo the work without ability to reciprocate and potential trust and collaboration issues.