Most large software projects include vendors, if that is not the case for you and you have your own development teams delivering everything, then you can just swap vendor with internal team.
Is it better to hire external consultants for accessibility assessment or is it better that it is made by the software vendor? I would say that both has its pros and cons and that combination works best.
my conclusion.
Vendor evaluating it’s own deliveries
I think that accessibility evaluation should be build in the deliveries from start to end. And it should be there from the design process not just when developing. Therefore this should be seen as an opportunity with best cost benefits. When vendor makes care smallest parts are accessible it is also easier for whole pages to be accessible.
When it comes to self-evaluation vendor is equipped with domain knowledge and therefore has both advantage and disadvantage against external auditor. Advantage is the time saved for transferring the domain knowledge and disadvantage is that it may also lead to missing the wrong turns that new users may experience when using the page or application in question for the first time.
At the same time it is not always the case to have an accessibility specialist on the vendor side, although I am a strong believer that every vendor should take all measures to have at least basic knowledge of accessibility – otherwise it is not possible to guarantee compliance and may lead to enormous costs.
So – some vendors may choose external help for this – which is not perfect but better than not focusing on delivering accessible products at all.
Vendor should therefore invest into it’s own accessibility literacy and skills and it will benefit both customer and vendor on the long run. If vendor is also involving disabled users to plan, produce and test it’s products when delivering them to the customer it has the best long-term effects on the overall usability and accessibility.
And I have to explicitly mention that self-evaluation should be honest and sincere also providing remediation examples and risk analysis.
External accessibility audit
There is a domain knowledge learning curve that has first to be accomplished in case of advanced applications, and it will take time and effort and even take down the productivity of the developers when they need to support the auditors.
External auditors that specialize in accessibility have a huge advantage when they include groups of specialists and groups of users with different disabilities that they cooperate with. I see this and the long experience track as the biggest advantage. But we must be aware that evaluation is a one-time task and when our products evolve and are being continually changed and updated we should be aware that it is difficult or at least costly to involve external auditors in every sprint.
Ideally there should be a combination
When vendor is taking it’s accessibility deliveries seriously, from design phase to development and testing phase – it will most likely yield best end results. If we combine this with an external accessibility specialists and more importantly with testers that use different assistive technologies on a daily basis – we can rest assured that our product will be as accessible as it can get. And that our evaluations will pass.