My wife and I first discovered this when we had some leftover marble
figurines.
We had brought many of the hand-carved animal figurines back with us
from Mexico. After a summer selling them for $7 each at flea markets and
craft shows (alongside our other products), we had some unsold pieces.
A friend mentioned that there was a new business in town, a service that
sold things on E-bay for customers. I dropped off five pieces  and
filled out a simple form. They did the rest. They took the necessary photos,
listed and auctioned off the figurines on E-bay, took out the fee for their
service, and sent me a check a couple weeks later. If I remember correctly,
after the fees, the check was for only about $10 or so.
That isn't too exciting, but on the other hand, at that time we were able to
buy the  figurines for a dollar each (they normally retailed online and
in gift shops for $12 to $20). I did no advertising, packaging or shipping, so
it was easy.
Now, it wasn't enough to motivate me to start a business selling these on
E-bay, but it does suggest some possibilities. After all, there are probably
some products that auction off closer to their retail value, and can be
obtained cheaply. For that matter, maybe a different service would have
been able to get twice as much by listing our carvings differently.
One way to make money with this idea is to do a kind of garage sale
arbitrage. Start by visiting a dozen garage sales with a notebook. Make a list
of things that are commonly sold in your area. Find those items or similar
ones on E-bay and see what they are selling for. Put those sales prices (the
averages) on the list. Determine what the fees will be for a Trading assistant
to sell them for you, and what other costs you'll have (gas for the car).
Finally, start shopping every weekend for sell able items. Make offers on
things that leave you with room to cover your costs and make a profit. For
example, if a certain type of doll sells regularly on E-bay for $13, and the
fees will be $3, you might offer $3 for any such dolls, which leaves you a
decent profit.
As you make mistakes and have successes, you'll learn what kinds of things
are easiest to find and sell, and you can concentrate on fewer categories of
items. With this kind of business, you don't have to do any work on E-bay
(other than watching auctions to get educated on prices), nor any packaging
or shipping. You just go shopping at rummage sales and perhaps antique
shops and junk stores, and then drop everything off at the office of the
trading assistant. They do the rest, and the checks are mailed to you.
Not all certified E-bay Trading Assistants have offices. Some operate from
home, and others do this as a sideline to another business, like a gift store or
antique shop. To find one in your area, go to E-bay.com and search for
"Trading Assistant Directory." You can enter your zip code and find the
ones nearest to you.
A laptop computer might help. You can tap into open wifi connections to
check for sales prices on e-bay while you are looking at items, or at least
without waiting until you are home.
There are a couple problems to note here. First, this is certainly not residual
income. You make money only as long as you work. Second, the income
you can make is limited by the time it will take to look for things and
deliver them to the E-bay Trading Assistant. On the other hand, this could be
a fun way to spend weekend mornings while making some extra income.
To boost your per-hour income, note which items make the most profit,
which types of rummage sales are best, and then skip the rest. There are
some potentially big spreads between what you can pay and what you can
sell for on some items. I met a man who regularly sold things on E-bay, and
he said he paid two dollars for a pair of jeans that he sold for $250. I was
skeptical until I logged onto E-bay that night and saw similar jeans selling
for even more than that.
One last thought: Even if you have no interest in doing this as a business,
now you know how to get rid of the old and unused things around your
house. Just drop them off with your local E-bay Trading Assistant.