Theory:
We are likely to value third-party consultation as objective, confirming, and without motive.
Application:
When we read reviews of 3rd party experts/ consultants, we value that information as being more objective and trustworthy. So besides testmonials of your customers (see Social Proof), can you get some external experts to review or talk about your services on conferences or their blogs? Even when you pay them to write a review on their blog and tell the audience it'll still work (example: sponsored review on Yoast.com). Of course it helps a lot if the review is positive ;).
A hierarchy of evidence (or levels of evidence) is a heuristic used to rank the relative strength of results obtained from scientific research. I've created a version of this chart/pyramid applied to CRO which you can see below. It contains the options we have as optimizers and tools and methods we often use to gather data.
This is a bonus episode with Emily Robinson (Senior Data Scientist at Warby Parker) en Lukas Vermeer (Director of Experimentation at Booking.com). In her earlier session that day, Emily said that real progress starts when you put your work online for others to see and comment on which in this case was about Github. Someone from the audience wondered how that works out in larger companies where a manager or even a legal department might not be overly joyous about that to say the least so I asked Emily about her thoughts on that. Recorded live with audience pre-covid-19 at the Conversion Hotel conference in november 2019 on the island of Texel in The Netherlands. (oorspronkelijk gepubliceerd op https://www.cro.cafe/)