Volunteering free time to a prospective seller?

I have a client that is conducting a local search. He understands that he's unlikely to differentiate himself from an experience or capital perspective but is exceptionally smart and personable. He also has the luxury of not needing to earn income right now. His idea is to volunteer some number of days or weeks to really get to know the business owner, the business, and demonstrate how can can bring value as potential buyer.

Is anyone familiar with an approach like this? If so, was it success or do you have any guidance on how to make this short-term arrangement most success for both parties? At a high level, I found it to be a creative win-win: an unexperienced buyer gets his foot in the door, the owner gets free work/perspective, and they both get to know each other better.