Make your search specific
Combine the type of business with a neighbourhood and the results get much more relevant: “independent coffee shops in Clifton, Bristol” rather than just “café”. In a big city, go area by area, because a single search only returns a short list.
Judge fit from the website
Star ratings and review counts on their own don't tell you much. Look on the website for signs of the problem your product solves: no online booking, a menu that's only a PDF, a contact form that doesn't work.
Write to the right address
The general address on the business's website (info@, hello@) is usually the best place to start. Addresses with a person's name in them may fall under different legal rules.
Using the data
Storing and reusing map data is governed by the platform's terms. Keep only what you need to make contact, and only for as long as you need it.