Run any idea through these five. Zero or one fail and it is worth trying. Two or more and it needs adjusting first.
1. Can they start within two weeks with what they already have? If it needs a purchase, a permit, or a skill they do not have, it is a later idea. Momentum matters more than optimization at the start.
2. Can they physically reach the customer? Walking, biking, or a parent already going that way. A business that depends on a ride your kid cannot arrange is a business that stops the first busy week.
3. Do people already pay someone for this? This is the most useful test on the list. If neighbors already pay for lawn care, your kid is competing rather than educating. Creating demand is hard for adults with budgets and impossible for a kid with a weekend.
4. Can they finish one on their own? Start to finish, without you doing a step. If you have to do a part, it is your business with a helper.
5. Would they still do it the fifth time? Ask directly. The first job is exciting for anyone. The fifth one is the actual job, and that is the one that tells you whether this lasts.
The tests are deliberately unglamorous. Almost every idea that passes all five is a service, close to home, that somebody is already buying.