As a teacher in a cash strapped district, I have to purchase my own supplies.  Ebay is the way to go. 

Here are a few guidelines to purchasing cartridges on ebay which work consistently.

• Go genuine.  Always put 'genuine' in your descriptor.  Refills and refurbished cartridges may or may not work..often they work for a shorter time and you lose what you save by buying more.

• Look for package color and expiration date. Companies change package colors and if the package pictured is of an unknown type, the contents are older. Cartridges work consistently for a year after the expiration date and the best deals are found on year old cartridges.  If you purchase one older than that, don't bid very high. Always inquire if expiration date is not listed.

• Look for sellers who list multiple cartridge listings and ask about combined shipping. Do this before bidding. If there is no response, don't bid.

• Avoid sellers who mislead by listing at under a dollar and charging exhorbitant shipping rates. They are not only attempting to cheat you they are trying to cheat ebay.

• With printers which use multiple color cartridges, attempt to find single color listings first..when buying a set, one frequently buys colors not needed. (I have a backlog of black cartidges which will probably last me way past the life of my printer!)

• Report any sellers who attempt to pass refilled cartridges off as new.  Clues to this are cartridges without seals,  worn looking casings, and removed boxes.  Granted many sellers remove boxes for shipping but I always check feedback before purchasing cartridges which are displayed with boxes and advertised to be shipped without. A dead give away is someone who has purchased empty cartridges recently.  This can be found in feedback rating list.

• As with any listing, check feedback and other items listed.  A seller who is selling one ink cartridge and other items, usually is honest. Someone who sells every cartridge with a claim to have just sold his printer should be investigated further.

• Check prices of cartridges currently on the market.  I questioned a seller once who was selling over the cartridge retail price and he replied that he didn't know why it worked either but people were purchasing!

• Sellers with zero feedback may be a bargain. However, check history of the seller to make sure there haven't been name changes.  This often indicates prior poor feedback. Keep your bidding low.  You are dealing with an unknown agent and your positive feedback is needed. Often honest new sellers will go the extra mile to obtain positive feedback.

Many of these suggestions are common sense to any experienced ebay buyer but they will be valuable to anyone without extensive experience.  Better learn from the mistakes of others than to make your own!