Every supplier in this field says the same six sentences on their homepage, so comparing them on the marketing is impossible. Four things do differ, and all four are askable in one email: the sample they will open, the passes they will run, whether findings carry criterion references and reproduction steps, and whether the retest is priced. This page is that email, and the arithmetic to hold the answers against. On the worked example the audit is $3,480 and the retest $1,392, so a quote with no retest line is a quote missing a quarter of the job.
Ask what they will actually open
How many pages, chosen how, covering which templates and which interaction types. A supplier quoting a flat price without asking your page count has not scoped anything. On the worked example 8% of 240 pages is 19 opened and 220 unseen, and both numbers belong in the report.
Ask which passes are included
Automated, keyboard-only, screen reader (which ones, on which browsers), 200% zoom and 320px reflow, and whether any user testing with disabled people is included. The last one is the clearest quality signal in this market and the one most quotes leave out.
Ask what the findings look like, and what the retest costs
Request a redacted sample report before signing. Findings should be grouped by template, carry a criterion and a reproduction, and rank by impact. Then ask for the retest as a separate line: on the worked example it is 40% of the audit, and a supplier who will not quote it is not planning to check their own work.
Questions people ask about digital accessibility companies
Is an overlay vendor an accessibility company?
They sell a different thing: a run-time script rather than an audit and a fix. Compare them on what they change, which is the page as rendered, not the code you own.
Do we need a company at all?
Not for the first pass. The free sheets and a scanner get you a long way; buy the independent judgement when you need evidence somebody else will accept.
How do we check a supplier's own site?
Run your scanner over it and tab through it. It is a fair test and it is surprisingly informative.