I used to buy and resell clothes.
Usually the cocktail dress type from Karen Millen, coast, etc.
Someone would chuck it on their unmade bed, photo it and advertise on ebay as 'worn once, needs dry cleaning'. I'd buy for under £10, often under £5, dry clean, take proper photos and measurements and put back on ebay with a buy it now of £50. I'd sell at least 10 a week, huge money spinner but very time consuming.
Unfortunately I must have been just ahead of the curve, after about a year there were loads doing the same which increased the purchase price and decreased the selling price.
I moved onto matched betting and casino offers and made over 30k a year on that, again it was near enough a full time job and I was only slightly ahead of the curve so it died after a few years too.
I dont have any new ideas but if you're a crafty person get along to an artisan market in a middle class area and see what's selling and think about how you could do it better.