To vet a supplier properly you do three things in order: verify the business actually exists and does what it claims, test them with a sample and a deliberately detailed conversation, then structure the first order so a failure costs you little. Most supplier...
The short answer: dropshipping is the cheapest to start and the hardest to defend, private label costs the most upfront and is the only one of the three that builds a real brand asset, and print on demand sits between them with almost no inventory risk but...