Do Google ads work for small businesses?

The size of a business is not a restriction for Google Ads. Of course, a smaller business might have a smaller Ads budget, but this is where your strategy has to be right for Google Ads to work. Smaller businesses that have a more focussed target audience and have more specific or local keywords will find that there is less competition, which means they can own that part of the market and effectively get ROI from ads.