My startup works with small businesses. I've been amazed at the amount of income that good service professionals can bring in. Landscapers, air-duct cleaners, carpet cleaners... we have a couple of clients that have owners pocketing 7 figures yearly.
What I find really interesting is how much the process these really successful owners use mirrors what we do in technology companies. They try different pitches. They test different call-answering tactics. They hone in on the words, phrases, and ideas that resonate with customers. They test different advertising metrics and are obsessed with tracking and analytics.
Once they understand how to close deals and what the best sources of leads are... they scale. For instance, one of our air-duct cleaning partners (that clears 7 figures in profit) has grown to four crews and a full time booking agent. The booking agent is extensively trained and closes 60-70% of all leads. The owner spends her time focused on quality control of the actual crews for the most part.
The point being: There is PLENTY of room for small business owners to make a lot of money with manageable levels of scale. You still have to have a keen business sense... but outcome based decision making works no matter what business you run.