In a proprietary process, offer the business owner that you will pay half of a business appraisal, for instance up to $7,500.
This shows conviction, seriousness, commitment, and collaboration.
And, importantly, it helps ease the seller's nervosity around valuing his/her business too low.
The appraisal may help you during fundraising too.
In my experience, most appraisers undervalue businesses anyway ("let me smash a 4.5x multiple on an undisputed EBITDA figure").