I am not a regular buyer and seller on eBay, but I have been doing it for many years. I thought to write this so it can help somebody
The first thing to do if you want to sell something on eBay is to search for ads that are similar to what you're selling, and see how much money is being requested for them. Once seen, you should consider whether it is worth selling or throwing it away to trash. Keep in mind that in eBay is sold "everything", the things that seems incredible that they can be sold, but you have to think if it is a good idea to sell. If your eBay account has a lot of "positive points", it makes easier to attract bids for what you sell.
It is very important not have negative points, and if you have any of them, you must give a good explanation of why you do not deserve this negative points. eBay has tightened recently the issue of the negative rates, so people that have "easy trigger" for a negative rate will be stopped. If what you are selling is of great value, and you sell it in your own country, it is better to ship it with a transportation agency instead of regular shipping. Open a Paypal account if you have not already, because more and more people use this payment system, the only downside is that Paypal keeps a small percentage of the transactions.
When is the best time to put something for sale? For me, Thursday afternoon, and making the sale to last 10 days. The sale will last 2 weekends (when most people buy) and also the sale ends on Sunday afternoon, when more people are connected to the Internet. The description data must be real and complete as possible, do not sell shoes without describing the size and other details. If you want to atract people, put the ad in Spanish and English, and put on sale for everyone (not just your country). Once placed the ad, answer the questions that the eBay users will ask about it, because they will be visible in the ad and will help more people to clarify things about the product you sell. Once sold the product, never send ir before you get paid. This seems obvious, but i have seen it many times.
This is a scary thing, giving money to unknown people and then wait anxiously to get the product. Obviously, the first thing is to buy only from people who have many positive votes, but verify that these positive votes are from selling, not from buying. Use a sniper. This is a website that has a program that does the bidding for you. You tell it what you want to win and it will make bids, with the peculiarity that the program will make your bid when the auction is only one second to complete, so no one can overcome and you will win the product. They are payment services, yet affordable. My favorite is "keecua" where they charge you $1, only if the program wins the product. Go for products whose auction ends at inhospitable hours (using the sniper this is possible).
Many people do not calculate the time of finish of their product to be offered for sale, and sometimes it ends in hours "after hours", where there will be little competition (unless you sell to everyone in the world, or the others go with snipers). Consider the issue of customs. If shopping in USA, Switzerland, etc..., you know that your product will probably end up in the local customs, so you have to add VAT to the total cost (18% is now?) plus Border Fees (another 4%).
How to avoid falling into the customs office? It is a completely random thing. If the product is sent by agency, it surely fall. If it is sent by mail, it may or may not fall. To avoid this, it is best to buy in the European Union, where there is no customs. Many years ago, when buying in the U.S. you had to ask the seller to write on the sheet of "customs" that the product was a gift, the famous box of "gift", this way you can avoid the customs office, but i do not know if it still works. If you are good repairing things and you like the risk, buy electronics that do not work, because often the only have a software glitch and obviously they are sold much cheaper. This is risky yes, but the risk is pleasure, right? This way i bought my first iPhone 3G, it was just in DFU mode (!)
Once purchased, do not despair (or do :-)). I have bought things that have taken up to 2 months to arrive, I remember I bought an Asus EEE to an Australian boy, poor man, i was informing eBay when suddenly the product arrived. eBay protects the buyer? personally I do not know, because I never had problems with purchases or sales, but I have read a lot of problems of other users with eBay. One thing is certain: If an item is too cheap and looks like a scam, 99% of the time IS a scam. Never, ever accept a deal outside of eBay, if an eBay user writes to you and says he has seen you bid on the product X and not win, and he offers this product to you very cheap outside eBay, that 100% of cases it IS a scam. And never buy products that appear to be imitations (for the price or whatever) but in the description does not say nothing about to be an imitation, in most cases are imitations.