eBay Trader
What you'd actually do
The work is sourcing items, researching what they will sell for, photographing and listing them well, answering buyer questions, and packing and posting orders. A good eye for value, honest descriptions and reliable postage matter, since your feedback rating makes or breaks repeat trade.
You are self-employed, so income is uncertain and depends on what you find and sell, with no wage, sick pay or holiday, and you carry the cost of any stock that doesn't sell. It can start as an evenings-and-weekends side hustle and grow, but it takes graft and patience.
No qualifications or licences are needed, but you must register as self-employed with HMRC once you are trading regularly and handle your own tax. Most people learn by doing, starting small and building up experience and feedback.