No certifications. There isn't even one that I know of that would apply, but they're all unnecessary in the electronics industry anyway. License wise you need nothing as long as it's considered a hobby or kept off the books - Craigslist, Facebook groups, local flea market... as long as you claim the items are yours personally (which they are once you buy them) and it's not a huge source of income for you, you should be fine. Once you get bigger if you open a retail store you'll need a vendor's license, but that's it. That way you charge sales tax and turn the sales in to the gubberment.