eBay can yield good prices for your offerings if you can build confidence and trust in the minds of potential buyers.  A good feedback record certainly helps this process and, until you have built one, you may be a little disappointed in your auction realizations.  The author is a collector, not a dealer, and has sold hundreds of US stamps for good prices over the years on eBay.  The author has learned that there are some practices that yield better results.

With or without a feedback track record, you can get better prices for your US stamp offerings on eBay by following some simple rules:

• Your item title will draw users into your full item page.  Put all the important information in the title: Catalogue Number (Scott for US stamps), mint or used, Condition (following Scott guidelines for centering), color variety (if any).  Add any appropriate information such as unusual cancellations, etc.  Many potential buyers appreciate seeing the current Scott catalogue value in the title as well since it saves them the time of looking it up.  Since many potential buyers use eBay's 'Search' to find items by catalogue number, avoid putting extraneous numbers in the title (such as your inventory number, the year of issue, the denomination of the stamp, etc).  You can put the catalogue value in the title as 'CV10' (for $10) in order to avoid creating an item that is found whenever a potential buyer searches for Scott #10.
• Be sure your item is listed under the appropriate category.  eBay's listing processes make it far too easy to place an item in the wrong category (usually by defaulting the item to the same category as the previously entered listing).  In particular, note that the 19th Century covers the years 1801 to 1900.  There seem to be a lot of sellers who seem to think that any year starting with '19' is in the 19th century!
• Specify the catalogue number correctly.  The catalogue number of the first airmail stamp is not 'C-1' or 'Cspace1', it is 'C1'.  Catalogue numbers do not have spaces or hyphens.  If you list the stamp as 'C-1' or 'Cspace1', that buyer who is using eBay's search to find the C1 that they want to add to their collection will never see your item!
• Don't exaggerate the condition of your offering thinking that you will get a higher price.  You will only cause potential buyers to distrust everything and anything you have to say about the stamp.  And describe any faults that exist.  If you don't, you will just get a lot of returns and negative feedback.
• Provide a high quality image in an appropriate size and in an accurate color.  Black backgrounds work best because potential buyers can most easily discern the condition of the margins and perforations against a black background.  Use an image size that is large enough to allow the viewer to see the details clearly.  This is particularly important when selling classic US stamps since many potential buyers of these items may be trying to identify such things as plate markings, cancellation specifics, and quality of the impression.  But don't make the image file so large as to take forever to download.  Many eBay users are still on dial-up connections.  If the image is too large, they will move on before they even see your offering.  For stamps worth more than $10, an image of the back of the stamp will also help potential buyers to evaluate your offering and will build trust.
• Use a scanner, not a camera.  Unless you are an accomplished photographer with a close-up lens, you will get much higher quality images using a scanner than using a camera.  And avoid the temptation to 'tweak' the image.  Attempts to adjust the color or contrast are generally detectable by knowledgable collectors.  They know what real stamps look like an will not trust you if the paper is too white or the color is too bright.
• The longer your listing the better.  Only one thing will yield you a good price: lots of bidders.  Short auction periods won't give potential bidders the time to see your item.  Nobody can visit eBay every day to be sure that they don't miss stamps that they are seeking.  I suggest that a 7 day auction should be the absolute minimum listing period and that 10 days is preferable.
• Avoid eBay promotional periods.  When eBay has 'specials' (such as a $.25 listing day), there is such a flood of material that you will more than lose the fraction of a dollar that you save with the listing because of lower final prices.  The same holds true for the week following the promotion.  There is so much material available during these periods that fewer potential buyers will see (and, possibly, bid) on your item.
• Don't use an image for text information.  Images containing only text are generally large and will simply slow the download of the complete item page.  Expressing text as html in the item page results in much faster item page downloads by the potential buyer.  Furthermore, most text in images appears less crisp and readable than the same text expressed as html.
• Start the bidding at a minimal amount.  Unless the item is not worth more than a few dollars or is so obscure that it is unlikely to draw many bids regardless of price, start your bidding at a minimal value.  (I start my offerings at a penny...and I've sold stamps at in excess of $1000 this way!).  There is nothing like a lot of bids on an item for attracting even more bids.
• Offer a no-questions-asked refund.  This will overcome any concerns of a potential buyer regarding the item.  You will get hardly any returns unless you have misidentified or mis-described the items.
• Educate yourself so that you don't misuse philatelic terms.  NH (never hinged) is a term appropriate only to unused stamps having gum.  Don't get creative with your abbreviations; stick with the conventions.  There are several eBay Guides to stamp abbreviations.
• Offer extensions.  For more expensive stamps, consider offering extensions for certification and state clearly who pays the costs in the event of an adverse opinion.
• List your memberships.  If you are a member of any philatelic organizations, say so in your item description.  Potential buyers are more trusting of sellers who are members of philatelic organizations.

eBay can be a great place to sell your duplicates and items that no longer fit your collecting interests.  By following the suggestions above, you will encourage potential buyers to trust your offerings.  The result will be generally good prices for your stamps that will generate cash for further investment in your collection.