SafeHarbor are the eBay police department. If a buyer does something they're not supposed to, then it's SafeHarbor you should be reporting it to.
Non-paying Buyers.
This is the most common rule buyers break -- it's all too easy for them to just change their minds and try to get out of the auction. eBay, however, regard every auction as a contract. They will punish the buyer for you if they don't go through with their end of the deal, by giving them a 'strike' against their account. A buyer who doesn't consistently doesn't pay for items they win will probably get banned.
To report a non-paying buyer, you need to file an 'Unpaid Item' dispute, which you can do here: http://feedback.ebay.com/ws/eBayISAPI.dll?CreateDispute>http://feedback.ebay.com/ws/eBayISAPI.dll?CreateDispute. All you need is the item number. Once you do this, eBay will send the buyer a reminder that they must pay for the item they won, wait a while, and then take action against them. You must wait 7 days before you can file a dispute.
This isn't that helpful to you, of course, since in most cases you still won't get paid for the item or have anyone to post it to: it is a rare buyer who responds to eBay's threats and pays up just to avoid a little warning from eBay. You will, however, at least get a refund of your final value fee and be able to relist the item for free - and you can send a second chance offer to someone else if you want.
Auction Interference.
If someone ends up with a grudge against you, then you might find that they start emailing your bidders and telling them that you're a scammer, they should cancel they bid, they shouldn't deal with you, and so on. You might even find that you have unscrupulous competitors who will try this tactic to get buyers to bid on their auctions instead!
SafeHarbor will investigate this for you - the procedure to report it is to click 'Help' on the toolbar, then 'Contact us' from the menu. This can be a bit of a maze: you need to choose 'Report problems with other eBay members', then 'Problems with buyers', then finally 'User is emailing buyers to warn them about seller or item'. This will then let you send SafeHarbor an email.
Feedback Extortion.
You might find that someone tries to intimidate you into giving them something using the threat of negative feedback - in its crudest form, this could be as simple as "Pay me $20 or I'll leave you a negative comment".
To report this to SafeHarbor, you should also use 'Contact Us', making sure you attach all the emails you have that prove the extortion happened.
You know, if it's not one thing, it's another. Maybe you're not be having all that many problems with the buyers you do get, but you seem to be having a problem with items that just don't sell. Never fear: the next email will give you some hints on what could be going wrong.
About the Author
Kirsten Hawkins is an Ebay and internet auction enthusiast from Nashville, TN. Visit http://www.auctionseller411.com/ for more great tips on how to make the most from Ebay and other online auctions.