1. Listing your item in the wrong category.

Most eBay shoppers look for items based on the categories in which they are most interested in.
A poor category choice can make it much more difficult to sell your product. If you cannot decide on a single category for your item—or if it is equally at home in two different places—pay a little extra and list it in both. Cassini notices if the item is listed in the wrong category. Since the histograms are deferring per category, only the items's right category makes the buyer able to find your item. Especially the subcategory “other” makes ebay see that you have no clue what you actually want to sell.

2. Lack of descriptive text.

Although it is imperative to have high quality photos ( minimum 1600px, maximum 12 pictures) to help influence shoppers, it’s more important to provide enough descriptive text to “romance” the buyer into taking action. A picture alone will not sell your item. You also need a concise, but complete, description. Put yourself in the position of your potential buyer and provide enough information, in terms of features and benefits, to make him or her feel secure in buying from you. There is a fine line between providing just enough information and too much. Remember: it’s quality, not quantity, that counts.

3. Not keeping your integrity intact.

A common mistake when you’re starting out selling on eBay is to create fictitious traffic and interest in your auction items. Some sellers actually create additional profiles and bid on their own auctions in order to bump up the selling prices of their items. Others encourage their friends and family to do the same. In either case, this is simply wrong, and you will be in violation of the rules. eBay calls this shill bidding and it is not only against their rules, but also against the law. This practice is unfair to other buyers and opens the door to other possible legal issues. With the fictitious traffic sellers get only visitors that don't buy the items, which affects negatively on their ranking and visibility on eBay.

4. Drop shipping merchandise.

Many sellers argue that drop shipping is a very bad idea. For example, you have a wholesaler who is shipping the items directly to the customer. You order 100 items, the supplier has it on stock and you get sold out all of them. In the same time, customer orders 10 more items, and when reaching your supplier, you get the news that is out of stock. Or that it doesn’t have the size or color you need. When this happens, sellers can’t fulfill their order, because that they don’t have the control of their stock. You might have made 100 good deals, but not fulfilling one may cause you a lot of problems and loosing your account.
Drop shipping is a very common topic of discussion. Decide what is better for your business model, and when using drop shipping pay attention to the reliability of your main supplier.

5. Combining orders.

Imagine the following scenario: You get orders during the weekend and send them on Monday morning. After you finished with your shipping, you get new orders. Meanwhile, same customer buys two different items the same day. In order for to save money on shipping, you choose to pack them together and send it on Tuesday morning. This is not a bad idea, but what can usually happen is getting the customer complaining that got two items with the same tracking number. Another situation that may occur, the customer can say that received only one item. So, combining two items send to the same customer, might save you shipping money. Unless you know well your customers, be aware of scams. Their complaints of not getting one of the items (which is not true) will get negative feedback and effect on the metrics.

6. Mistyping counter offers.

It is not a big mistake to make, but it will certainly cost you a lot of money and it can tick off a customer. For example, you listed an offer for 50 GBP and your customer offers you 20 GBP. Then you go on by saying that can sell the item for 35 GBP. Accidentally, instead of 35 you mistype 3,50 GBP, and the offer is accepted, means the item will be sold for only 3,5 GBP. If the order is cancelled, will lead to bad feedback, getting a cancel order, destroying the metrics etc. Two ways to solve when this happens: either send the order and lose money, or cancel it and lose metrics. In order to prevent that, always pay attention when typing counter offers and check it before clicking agree.

7. Not properly or fully describing the items.

Good title and description will provide you with a clear picture of the product and attract more customers to buy it.
Not including sizes, colors and condition will only make your listings not visible on eBay search rank and most probably get you negative feedback, return orders requests and money. In the long run, you fall below standard selling and will cause to get suspended and losing your account. It is very easy to fix. You just need to spend some more time on the descriptions and include everything such as:

• Organizing information in paragraphs with similar information grouped together.
• Start with the most important details that buyers need first, such as additional details about your item.
• Include specific information like size, shape, color, age, manufacture date, country of origin, company/artist/author, and notable features or markings.
• Clearly state the item's condition, such as new, used, or still under warranty. Be sure to mention any flaws or repairs.
• Be clear about what's included and the type of packaging.
• Make the description as readable as possible.
• Include your return shipping policy for international returns, if it's different from your return policy for buyers located in your country.

8. Sending orders by putting the wrong label.

It can happen even to the best! white Sometimes sellers get similar orders, and accidentally put the wrong label on the order, or the wrong item in the package. This can be fixed by contacting the customers, and manage to exchange the items. But, it can also cost you minimum 2 negative reviews. So, always double check the orders you are sending out, and the labels you put in them!

9. Accidentally not choosing the eBay Global Shipping program for international shipping.

This is a serious mistake that eBay sellers make, but at the end of the day it will cost you only shipping cost money. Many of them when want to ship globally, forget or avoid enabling the Global Shipping program. If your item is located in the UK and you're shipping to an eligible country, you should use Global Shipping Program. With the Global Shipping Program, you ship the item to a UK shipping center, and international shipping experts manage the international shipping and customs process for you. Otherwise, it can cost you money. For example, you got an order of 10 GBP with free shipping and needs to be shipped to Spain. Shipping it on your own, will cost you 20 GBP. Using this program will have your shipping cost calculated, and it’s not your responsibility to check on import duties, taxes and charges. On top of that, you will avoid cancelling orders, which can influence your feedback.

10. Under calculating or not calculating right the shipping cost.

It is always a good idea to find out how much it will cost an item before you list it on eBay. One of the most common beginners mistake on eBay is wrong calculated shipping costs. Even worse is not even calculating it. It’s an easy mistake, but on the other hand can cost you losing money, time and getting bad reviews. Fortunately, it can be easily corrected, so your shipping costs are set right. Here is an easy way to calculate:

• Pack your item.

  Practice packing your item, as you would send it to the customer without completely sealing the package.

• Weigh and measure the item.

  When determining the shipping costs, accurate measurements are really important. For items weighing less than pound, use a postage scale or food scale. For items weighing a pound or more, you can use a regular bathroom scale. For the size, measure the length, width and height of the package( in inches).

• Use the eBay Shipping Calculator

  Take the advantage of using the eBay Shipping Calculator for free. Just enter the size (measuring the shipping package, not the item itself) and weight. Then select a sample destination, to get estimates for a number of different locations. The calculator will give you an estimate of your total shipping costs, for a variety of different carriers.