To do an audit you have to audit against some sort of pre-established criteria. That is how audits work. In security, that will typically be a standard (or set of standards) alongside a threat model. In finances, you audit against what is legal in the areas you operate.
>[...] zero idea what the auditor would be doing?
That's a practical impossibility. From the client side you want to be able to evaluate quotes, stay within a budget, etc. You don't want to pay good money (audits are really expensive!) for areas that you are works-in-progress, or non-applicable threat models (e.g. lots of security software explicitly does not protect against nation-state actors, so they don't do audits from the perspective of a nation-state actor).
From the auditor side, you want to know what staff to assign (according to their expertise), how to schedule your staff, etc.
>If Mullvad dictated how to do things or imposed limits on the reach of the testing, the results are worthless anyway
Not at all. The company says "This is the set of standards we are auditing against and our threat model. This is how we performed". The results are useful for everything covered by those standards and threat model. By explicitly stating the threat model, you as a consumer can compare your threat model to the one that was audited and make an informed decision.
To do an audit you have to audit against some sort of pre-established criteria. That is how audits work. In security, that will typically be a standard (or set of standards) alongside a threat model. In finances, you audit against what is legal in the areas you operate.
>[...] zero idea what the auditor would be doing?
That's a practical impossibility. From the client side you want to be able to evaluate quotes, stay within a budget, etc. You don't want to pay good money (audits are really expensive!) for areas that you are works-in-progress, or non-applicable threat models (e.g. lots of security software explicitly does not protect against nation-state actors, so they don't do audits from the perspective of a nation-state actor).
From the auditor side, you want to know what staff to assign (according to their expertise), how to schedule your staff, etc.
>If Mullvad dictated how to do things or imposed limits on the reach of the testing, the results are worthless anyway
Not at all. The company says "This is the set of standards we are auditing against and our threat model. This is how we performed". The results are useful for everything covered by those standards and threat model. By explicitly stating the threat model, you as a consumer can compare your threat model to the one that was audited and make an informed decision.