Apple has a minimum distribution quantity of around $100,000, so that will give you an idea of the arena you are looking at playing in. You keep mentioning 'high returns', but you are trying to sell in the biggest online wholesale marketplace in the world, finding something new to sell that offers high returns is like finding rocking horse poo!
Even if you did find something, 24 hours later the other 3 million sellers would also be on to it and your margin would be stripped in an effort to remain competitive.
People do make money on ebay, but only a very rare few would make high returns on a particular product, if any at all.