How do you differentiate discontinued product versus ones that are upgraded to a different model?
I generally look for stuff where I make a small profit at current price and where total quantity isn't so much that I'm worried about getting stuck.
I look at a lot of things, and like I said I don't just do discontinued items.
Right now I'm holding onto some Samsung Blu-ray players from 2015. Samsung stopped making them, so the 2017 models are the latest, but the 2015 are cheaper and still selling quite well. I expect the price to go up a bit as the other guys selling it sell out, and then I'll make maybe 30-40% on my money for holding it for 4 months or so, minus costs/returns.
Very doable if you have capital and are willing to be active and take some risks.