Running a supermarket

Hi, as the title suggests can anyone who has run, still running or know someone who runs a supermarket give some insights. 1. What is your avg margin on the goods sold? Which goods have higher margin? 2. Is it profitable? If you dont mind, please share your operating expenses. 3. Which goods move faster and have a high demand than usual? Also please share any experiences or lessons you've learnt being in this domain. Thank you!