All over ebay I see sellers making the same mistake. They don't describe their items enough in their auction descriptions. Descriptions are what keep the customer there to buy. Your title brings them to your auction and the description draws them in to buy. Make sure you don't leave anything out. Even if you have to repeat yourself. Your description should jump out at the potential customers. Auction descriptions are almost as important as the product you are selling.
If your description has the name of the product but not the model number; then the customer will be unsure and probably not buy from you. Remember, you are selling the product online. The customer can't pick it up and read the package or know anything about what you are selling them, unless you tell them. This is probably the most common mistake sellers make. They don't describe the name of the item or model number enough. Model numbers may be very important to the customer to reassure them, that they are buying the right item. Make sure you examine the product package and put everything on your auction that is on the products box. If you can't see the product box, just goto the manufacturers website and get your description from there (don't copy and paste it, you may infringe copyright). Don't leave out any minor details. They may be minor details to you, but to the customer it may be very important. Make believe you are the customer. Make believe you don't know anything about this item. If you follow this simple tactic of listing the item name and model, you will take your competitions business away. You will be surprised how many sellers don't list these two very important things in their auction. Most of the time, customers search for either the item name or model number. So it wouldn't hurt to use a subtitle for this information as well.
Don't ever lie or exaggerate about what you are selling. Chances are, you will do more harm than good. There is almost always someone out there who knows more about a product than you do. They may shy away because they know you are not being honest in your item description. If you have damaged goods, tell them what is wrong with it. Otherwise you will be rewarded with a "big, fat, negative, feedback". Nobody likes a con-man that sold them what they didn't want. When the customer gets their item, they will know if it is not what they wanted. You can be sure, they will let you and the rest of ebay know about bad deals on your feedback.
Used or new is a very easy part of the description that lots of ebay sellers forget to mention. It's very important to the customer to know if they are buying new or used goods. I have shy-ed away from so many auctions because the seller didn't tell me whether it was used or new anywhere in the title or description. How can someone forget to list something so simple and needed? Is your price fifty dollars cheaper because it is used? This may be a question you find asking yourself when you look at an item description. I just skip these types of auctions now. If the sellers are not smart enough to list "new or used", then I am not sure I even want to deal with them. Believe it or not, you will steal your competitions customers away, if you tell your customers you have a used or new item for sale. Just because lots of sellers, selling the same thing don't say if its new or used.
Weight is another important factor always left out. The customer usually pays for shipping. Most people want to know if you are making a huge amount off of shipping. For instance, you may see a seller charging $100.00 for shipping, but it only cost them $30.00 to ship. There are other reasons the seller may charge a higher shipping price, but that's a whole other post. Weight may also be important so the customer knows, if they will need help moving it around or transporting it. Something as simple as weight, most sellers see no need to list this important information. They couldn't be more wrong.
I say the more description the better. You will have more sales by over describing something than not describing it enough. You can never describe something too much. Repeating all the good points of the item more than once is fine. Just in case the customer misses the first section. You will be surprised how many customers never read the whole item description. They usually read what they need, to reassure them they are buying exactly what they want and that's it.