What diligence providers have you worked with that do not charge for diligence? Or get creative/do a flexible diligence process on fees?

I am in the insurance space, and some charge a fee and some do not. Curious what other industries are structuring it the same way. And if so, has the experience been positive? There are times that there is a misalignment between management on expectations of providers and if they credit the fee up front what that means post-acquisition.