At any one time you can find thousands of LEGO auctions on ebay.  Some ebay LEGO sellers are experts in the field, while others are just trying to make a quick buck from something they found at a yard sale, but have no idea what it really is or what it's worth.

You can easily tell what kind of seller you're dealing with on ebay by reading the auction's item description.  Several people out there sell sets and mention that they've checked the list of parts for completeness by comparing it to what's listed on Peeron.com.  This is a good thing; it shows that the seller knows what they're talking about when it comes to LEGO.

Then you have those sellers who are somewhere in the middle.  They know the difference between LEGO and clone brands, but they don't know a whole lot about LEGO itself.  This caliber of seller would be the kind who calls Forestmen minifigs "Robin Hoods."

Finally you have the bottom feeder ebay sellers.  They might have a pile of Classic Space men and think that they're not worth much, because that don't look as "cool" as more recent MF's with more detailed torso printing.  On the other hand, they might have a pile of some common part that any slack-jawed yokel could buy on Bricklink for 3¢ a piece, and they list it as some kind of "rare collection."

Whatever the level of LEGO knowledge, any ebay seller can spice up his listing by doing 5 minutes of research on what they have and by making the listing fun to read.  Take an auction I saw for the 1993 Fire Breathing Fortress, for example.  The seller has this to say about the set:

"This set was originally released in 1993 and is no longer available.  It comes with 6 figures (a wizard, three guards, a mounted knight, and a wolfpack prisoner)  and a green dragon.  The set features an opening gate that leads to the dragon's cave, a jail cell, a moveable dragon head that drops rocks on intruders, and a trap door that drops unsuspecting ruffians into the dragon's den!  Hours of endless fun await the high bidder!"

The seller knows what year the set is from and lists the MF's that are in it.  This is a very good start.  "a trap door that drops unsuspecting ruffians into the dragon's den"--HA, I love it!  Instead of claiming that you can keep your kid occupied for hours on end, as many ebay sellers do with LEGO, this seller lists that "Hours of endless fun await the high bidder."  This seller realizes that it's most likely that some AFOL will win this set as opposed to a parent buying it for their kid.  The "Hours of endless fun" part may be a little over the top*, but that's what makes this auction listing fun to read.

* I actually timed myself as to how fast I could build this set when I was younger.  It took me 58 minutes, so I would have to pace myself to have "hours" of fun with it.