My niche for resale items: college textbooks
I've bought them for as little as 50ยข, with a resale value of over $75. Last summer one seller gave me a whole box of them. It was the end of the day and she didn't want to deal with them. I sold them individually for well over $125.
I sell textbooks both on Amazon and Ebay. And I almost never buy a dud! My secret weapon: my iPhone and a little piece of software called SnapTell. SnapTell is now available as an Android application, so you can use it on a variety of smart phones.
This little iApp is awesome! Even better... it's FREE!
You just snap a picture of the front of a book, dvd, cd, or video game and within seconds you get tons of details -- the most important for purposes of resale -- the price it sells for used.
To get the "used" price choose Amazon, then scroll to the bottom and you'll see the price range for Marketplace Offers.
That tells you approximately what the book will sell for. It helps, for textbooks, to also look at the date of publication. More than a few years old and you may have to sell it internationally to get any takers.
Plus, you'll want to consider the size and weight of the book. Really heavy books (like an art history book I bought), may cost only a couple of bucks and sell for $12, but Amazon has strict rules on what you can charge for shipping, and any extra charges are at the seller's expense. (Priority Mail, for instance - Amazon maxes the charges out at $6.99, for a heavy book you'll be paying the USPS at least $9.80.) The other option for the heavy books is to sell them on ebay; no standard shipping price.
Selling books on Amazon and Ebay is super simple. For the most part, all you have to do is enter the ISBN number and all the data is provided. Then, just customize your listing with details about the condition of your item and you're good to go.
If you're on a Mac, it get's even easier to list books on Amazon. An inexpensive application called Delicious
Library, handles most of the work. Using your iSight camera, shoot a picture of the bar code and the software will look up the book, cd, dvd, or video game and add it to your catalog. Then just right click on the item and choose: "Sell on Amazon". It couldn't get much easier than that!
Shipping
For most books, I ship them in padding envelopes. I reuse the ones I get in the mail and have supplemented my supply by shopping the sales at Walgreen's; they frequently have them on sale for about 50 cents each.
If you choose to sell online, I highly recommend you check into using the online service for postage such as Endicia or Stamps.com. You can also use the post office website, but you can't purchase postage for media rate parcels. Ebay, through PayPal, has a built-in shipping solution, which makes it very easy to ship, and you can choose from UPS and USPS. Most of the online solutions give you a better price on options than you'll get in person.
Selling online isn't for everyone. You need to be honest about the quality and condition of items you are selling. And you need to be prompt in processing and shipping orders.
Consider looking for textbooks the next time you're out bargain hunting. The best "season" for buying is a month or two after the end of the term, and the best time to sell is a week or two before terms begin (that's when people are looking to buy!).