Unfortunately very few sellers will NEVER go without one single complaint. Even the best sellers in the world!
The only thing you can do is try your best to make the customer happy. Remember the customer is always right (well almost)! The main thing you need to remember on ebay is that feedback is one of the main keys to success so protect it at all costs.
Obviously it's impossible for me to say that if you listen to this guide you will always have happy customers however, I can say that if you do follow this guide then hopefully you will reduce the amount of unhappy customers to a minimum.
The first thing you should do when you recieve a complaint is try and put your self in the customers shoes, if you can do this then at least you might be able to understand why they are unhappy. If what they are unhappy about is something that you can sort out, then do it. It's not worth risking getting negative feedback for something that you can sort out in a few minutes.
Remember you can always relist the item so dont be scared to give the customer a full refund. This should be your last resort!
Another reason you should always try and make the customer happy is that if they believe that you are trust worthy then they are more likely to buy from you again and possibly they might even pay a little more in the future because they know they can trust you. Remember, repeat business is GOOD BUSINESS!
The only other thing i would say is just becareful your not been taken for a ride. Unfortunately some people will try and take advantage of your good nature so always check there past history, use the feedback forum and dont be scared to contact ebay if you feel the buyer is trying to bully you into a corner.
Another tip is never leave the buyer feedback before they leave it for you first.
Just remember always make your listings as honest as possible and describe all goods clearly stating any damage they may have. If you do this then you should find buyer complaints few and far between.
Well thats is, i hope this information has been useful and Good Luck!