There are many things that make a well made purse vary from the el-cheapos. Many women already know this, but i'm sure there are some who don't.

Things to look for to indicate quality:
Stitching - is the stitching double stitched, and how heavy is the thread used? These determine how well the purse will hold together in the long run.

Hardware - the metal rivets, buckles, rings etc that the straps attach to. This includes zippers and zipper pulls too. What are they made of - nicer purses use more well stitched leather or heavier duty metal like brass or steel (not the "base" metal cheap watch cases and other junk is made from).

Does the bag have feet of some sort? Nicer bags will have leather tabs, metal studs, etc that go under the bag to protect the bottom from heavy wear.

Pockets / overall design - is it well organaized? Regardless of pocket design on the outside, interior design will usually have dividers and pockets to keep everything seperated - even bucket bags usually have a few if nicer.

Material - you definitely should expect heavy double canvas or leather from nicer brands. These materials can take abuse and hold up in the long run, so look for that Genuine Leather tag. There are even differences in thickness of leather, and thicker generally wears better. Some more expensive designers will still use vinyl etc, but its less used and I would avoid those models, they usually will not hold up.

Lining - the better lining is well stitched in, it won't tear lose for years if ever. The material is heavier, and able to withstand some wear. This even applies for satin, which is common material for lining - it does come in heavier versions, and it is in some of the nicer purses.

Things to look for when buying a used purse:
Does the purse have its original dustbag included? If so, this may not only be a bonus, but indicate if the seller took care of the item well - meticulous people who keep accessories and original packaging often take good care of what they own!

What kind of leather is it? Soft leather is more likely to wear and have small tears in it, hard leather wears on the edges and is more likely to show scuffs.

How is the interior? Is it clean, or are you going to need to vacumn, stain remove and sterilize? You will be surprised what some people will try to sell you, and no one wants to try to get used bubblegum out of a purse liner! If you have a cell phone make sure its got a poket for it.. With todays bags, almost all have them. And moreso, make sure the pockets aren't torn. If the auction doesn't have a picture of the interior, ask for one, or at least confirm its not dirty, the liner isn't torn, and the pockets are all still attached. Most importantly next to making sure the liner pockets and stitching are holding up, is the zippers. Make sure they all zip and do it smoothly, without snagging.

Is the hardware scratched up, cracked, or otherwise damaged? Make sure its nice and shiny (if originally polished and not brushed look).

Make sure the leather doesn't have heavy wear, cracks, tears, etc. Look at those pictures closely! Canvas should be clean without heavy stains, and watch for pulls as well as tears. If canvas has some leather sewn on, look at those stitches to make sure its holding up! You don't want to see threads or loose stitches.

If any doubts about any of these questions, it NEVER hurts to contact the seller and ask all these questions. Many times, you will be glad you did!