Available data differ greatly in relevance and reliability. Rigorous evaluation of environmental outcomes from commercial ecotourism products generally requires on-site audit with full access, internal and external documentary sources, and interviews with staff and third-party stakeholders; and even then there is no guarantee that the auditor has uncovered everything relevant. Many authors focus on place or management rather than companies or products, and do not distinguish between independent travellers and escorted tour clients. This applies particularly to the literature of parks and recreation management. Much of the literature is relatively uncritical. The same case studies are cited by successive authors, and achieve recognition simply through repetition, even if the original reference was actually written by a staff member, consultant or close associate of the organisation concerned (e.g. Nycander, 2002; Shah, 2002). In some cases the original material may have been simply a contribution to an unrefereed compilation; or a report with no pretensions to academic credibility; or an article which, though scholarly in itself, was not intended to test the claims or examine the achievements of the ecotourism enterprise concerned. Such sources may still be accurate, but they are less reliable. In addition, many authors continue to cite older descriptions of particular case studies without the caveat that they may no longer be valid. Small businesses can change quickly, in ecotourism as in other sectors; community enterprises can collapse, and donor-funded projects may not survive independently. The results presented in the following sections are thus tempered with a degree of uncertainty over data.