Just like a driver's license does not say if you are a good or bad driver, an ISO 9001 certificate gives no indication about your system robustness. Having access to audit records should be a way of making the supplier's system maturity more transparent to existing and potential customers.
They should read them because they requested it as part of due diligence.
If this is "due diligence" from a PROSPECT (I am intimately familiar with due diligence from my investment banking days), the only way I would consider someone elses's audit report if I were a prospect would be to compare it against my own, especially any internal audits. The difference is that in investment banking, we were very leery of scams and frauds, with cooked books and faked or forged documents. We were not especially concerned with "ignorance" since we would probably revamp a management team as part of an IPO, either educating or eliminating those we found ignorant of good business practices.
I CAN say that in 40+ years of business, I never met a business leader I respected who would have considered looking at someone else's report, especially a "self-created" one, without ALSO looking at and comparing with a similar report by his own employee or direct agent. Heck! As the ENRON case proved, even independent, well-respected CPA firms can have employees (auditors) who willingly aid a company's management in committing fraud.

Think of it this way - if you were suspicious of your spouse being involved in an extramarital affair, would you believe his/her word alone or seek independent corroboration by your own investigator?