So it's hard for you to find goods that are cheap enough to sell for a good profit? Now you're in the right place.
Garage sales. Most likely, you've seen ads for these most of your life and ignored them. Start attending as many as possible. You won't find good things at every one, but if you find one person with good things, make them an offer for the whole lot. They'll be so happy about it that you can get a great deal.
Markets. If there is a market near you, go there and see what you can find. You could buy it there if it's cheap enough, or you could try to make friends with the people who sell things at the market and find out where they get their goods.
There are pawn shops. Most of the time, pawn shops don't know what to do with the junk they get, unless it's jewellery. Most of the time, they put their stock on the shelves in a random way, hoping that someone with a little money will come in, look around, and buy strange things. Get them to give you a deal if you buy a lot.
Real auctions. Go to a real auction, because chances are you can sell things for more than they will sell them for. After all, they only have a few hundred people in that room, while you have a few million people to sell to.
The local papers. Put an ad in the local paper that says "I pay cash for [your item type]" and includes your phone number. If you can afford it, make it a large display ad so that people will see it.
Billboards. Get one of those small ads that you see in grocery stores.
Friends. Ask your friends if they want to sell you anything, and ask them to tell their friends about it.
Get noticed. Give people your business cards and tell them what you do. There's a good chance you'll meet someone who says "Oh, that's it? I have a bunch of [item] that I don't want ".
Shops. Some real shops sell things for less money than they do on eBay, which may come as a surprise. Take a look around your local deep discounter, and pay special attention to any shops that take trade-ins from customers. Chances are, they lose money on trade-ins as a promotion and want to get rid of that stock as quickly as possible.
eBay is the last thing. When you look at the completed items view, you'll see that eBay items can sell for a huge range of prices. Try searching for the most expensive item on its own, then sorting by lowest price: I can almost guarantee that you'll see an auction for the same thing where it sold for almost nothing. The trick is to find these bad auctions before they end, win them using a service called "bid sniping," and then sell the item again.
When you finally sell the item, though, after all that trouble, a buyer might give you a feedback rating that you don't think is fair. What to do will be explained in the next email.