Nice question.
Here is what I suggest:
1. Select 10 local businesses. Offer them 1 FREE* endorsement (see next comment).
* If this is too expensive for you, you can always add a condition that if the endorsement brings them more than x new customers, they pay the initial cost of the endorsement (so no profits for you, but it will cover your costs).
2. Have a local influencer endorse the business and make sure to track/measure (and photo) the positive affect. You offer this free for those first 10 businesses, on the condition that if it works they write you an amazing recommendation (you can even draft the recommendation and show it to them in advance so they approve it). Be sure to ask the influencer to mention a specific discount code so that you and the business will be able to track the success of the campaign.
3. Now, when you go to other / new businesses, you show them the proof that your method works (the letters of recommendation from businesses).
Make sure to have a short, simple, agreement with future clients. I've successfully helped over 300 entrepreneurs and I'd be happy to help you with the business and legal aspects.
Sounds like a cool venture. Good luck