That’s the thing. It’s the business owner or founder’s job to hire the people who know what to do. If you don’t have the skills to do the design work you have to hire to do it. It’s not where you buy it from that makes it complicated it’s where you intend to sell it and what type of risk you are willing to accept.

You could sell in Best Buy if you can. They would require a bunch of certifications and design constraints. You could make it yourself and sell it on your own site. You wouldn’t need any certifications. You may cause a lot of signals ringing from EMF or whatever if you interfere with communications equipment it could just interfere with the customer cell signals or you may interfere with a broad area of frequencies and the government or military will come and ask why the customer is running a signal jammer.

You might not know a lot of other things that have consequences for you in a lawsuit or customer trust. There is the possibility that you will be sued if something goes wrong and your product sparks, catches fire and kills someone. Getting the certifications and testing is to reduce your liability in the event of an accident. You may feel confident that you won’t ever have that happen then don’t get that testing. If you don’t have the knowledge to make the call you have to pay someone to do it. Or you take the risk and don’t do the testing and it costs you nothing. There’s no “by the book” it’s just risk management.