The first security questionnaire a company receives is treated as an event. By the tenth it is a recurring tax, and by then it is usually costing a week of engineering time a month and holding up deals at the point they are most likely to close.
The observation that fixes it
Questionnaires differ enormously in format and barely at all in content.
SIG, CAIQ, VSA and the bespoke spreadsheet a customer's security team wrote all ask about the same domains: access control, encryption, business continuity, vendor management, incident response, data handling, personnel security. The question count varies from forty to four hundred. The number of distinct facts about your company does not.
That means the unit of work is not the questionnaire. It is the answer.
Build the answer library first
Maintain a single set of canonical answers, each with:
The question it answers, in your own words rather than a vendor's phrasing
The answer, written once and carefully
The evidence that supports it, or a link to it
An owner and a review date
The review date is the part that decays first and matters most. An answer library nobody has reviewed in eighteen months is worse than no library at all, because it is confidently wrong and someone will paste it into a contract context.
The realistic failure mode is not a deliberate misstatement. It is someone answering "yes" to a question about a control that mostly exists, during a deadline, because the honest answer needs a caveat and there is no room for one in the cell. That answer is now a representation to a customer. ::
Answer honestly, with scope
"Yes" and "No" are rarely accurate. Most real answers are "yes, for these systems" or "not currently, and here is the compensating control".
Security reviewers are used to this and generally respond well to it: a qualified answer reads as someone who understands their own environment. An unqualified "yes" to everything reads as someone who did not read the question, and it invites follow-ups that cost far more time than the caveat would have.
Publish what you can, ahead of time
The cheapest questionnaire is one that never arrives because the reviewer found the answer themselves.
A trust page carrying your certifications, subprocessor list, data-handling summary, uptime history and a security contact deflects a meaningful share of inbound questionnaires entirely, and shortens the rest. For most companies this is the highest-leverage single page on the site.
When you get a bespoke spreadsheet
Some customers will not use a standard format. Two things help:
Answer their format, from your library. Do not maintain a second set of answers per customer, that is how two versions of the truth get created.
Ask which questions are blocking. A four-hundred-row spreadsheet usually has fifteen answers the reviewer actually cares about, and asking is generally welcomed rather than resisted.
The measure that matters
Track days from questionnaire received to returned. It is the number that shows up in the sales cycle, it is easy to measure, and it falls sharply once the answer library exists, usually from weeks to days, mostly because nobody is writing anything new.