• Ignore emails- nothing makes people more mad than when sellers ignore their emails or questions.
  
• Dont take pictures- people want to see exactly what they are getting.
  
• Write very brief descriptions- ebayers want to hear exactly what they are getting along with all your policies. If you fail to describe your item sufficently dont except bids to go through the roof
• Make Annoying listings- Lots of colors (especially flashing), CAPS, oversize pictures, pop-ups, and music make listings very annoying and take a long time to load remember there are many other sellers out there with simple but efficitive listings that bring in more customers
• Inflate your shipping- No one likes getting ripped off on shipping its not fair and its becoming a big problem on ebay
• Refuse to give shipping discounts- I never understood why sellers with multiple items won't discount their shipping on additional items that you buy from them doesn't make much sense
• Local Tax- Its ok to do it if you have a high volume of sales or you have to report this income on your taxes but if your an ocassional ebay seller why are you charging tax to local customers that's nonsense
  
• Refuse local pick-up- Refuse to give local pick-ups or better yet offer local pick-ups but charge a bogus "handling fee/charge" especially if the buyer says he/she will meet you anywhere
• Take a long time to ship- If people pay you fast you need to return the favor and ship them their stuff fast, be fair people want their stuff just as you would as a buyer

I just encountered this today I ask a seller a question just to make sure about something in the listing because its my hard earned money and they say ITS IN THE DESCRIPTION whats with that? I must be mistaken or something because I could have sworn sellers need buyers if its in the description just bite your tongue and politely answer the question without the sass or bluntness you dont want to do anything to piss off a potential buyer (which it has happen to me and i choose no longer to bid)