Dollar stores are full of, well, items priced at $1! Dollar Tree, Family Dollar and Dollar General all carry $1 items as well as some slightly higher priced items. You don't have to invest a lot of your money to turn these items into a profitable sale on eBay.
Visit your local dollar store and walk the aisles to get an idea of what they carry. Look for shelves with a lot of the same thing on them. These are likely discontinued items or items with package changes. It can be shampoo, makeup, barbecue sauce, books or just about anything.
Look for resale value. Is this item a name brand? Was the book written by a well-known author? Does the barbecue sauce have a well-known chef on the label? Is the shampoo form a large chain of expensive salons?
If you think there might be a market for it on eBay, buy one for research. Keep the receipt in case you need to return your item IF the store takes returns. This is one of the hazards of shopping at dollar stores, but since your investment is minimal ($1, right?) it is well worth spending the buck.
Bring up eBay's website. Type the name of your item into the search field. Does it come up? If not, type in a generic search for, say, blush. Then narrow down your search to the name brand of the blush, L'Oreal. If a long list comes up, try to narrow it down a bit more by adding on the color of the blush, like rose. The point is to narrow down your search without narrowing it down to no search returns.
Do any of the 'L'Oreal blush rose' have bids right now? Click on completed searches for final selling prices. Refine the search with the "highest price" option. What is the highest price your item sold for? Now skim to the bottom of the page or listings and check for the lowest price. Your item will probably sell for a price somewhere in the middle.
Noting what you paid your item, can you make a profit? Make sure you take into account eBay and Paypal selling fees. Can you still make a profit? What if you sell it in a lot of six? Or 12? Can you make a profit now?
If you can still make a profit, then you found a winner. Buy as much as you think you can sell at the dollar store, list it and reap the rewards.
Take seasonality into account. Buy sunscreen in January while you have a several months to sell it. Don't worry if it doesn't sell by summer's end as eBay shoppers buy year round. Can't afford to buy upfront? Then bring a pen and notepad and write down the details of your potential eBay items and do research at home before you buy.
If you buy an item with an expiration date, make sure it is for well into the future. Always buy the items before listing them on Ebay. What if the store sells out before your listing ends? Never tell employees or other customers why you are really buying six dozen bottles of shampoo. Just say you like to be clean. Why tell others your secret source of income?