Everybody has a garage pile they want gone, and nobody wants to haul it to the dump. Junk haulers charge by how full the truck gets, and one California operator who started with a used pickup now averages $549 a job. Apps like Thumbtack are where many of them find their first customers.

Dog owners love their dogs and hate the backyard. A Virginia couple started scooping yards before and after their day jobs in 2000, and DoodyCalls now has more than 100 locations. At about $18 a week, 50 regular yards comes to roughly $3,900 a month.

Most people would rather see the dentist than spend a Saturday at a car dealership. A former car salesman now charges buyers a flat $1,000 to do the haggling for them, and his company brings in about $200,000 a month. He started by doing 50 deals for free.