Generally, buying or selling items or services online is pretty safe, especially if you are selling or purchasing on Gumtree, eBay, or other well-known auction sites. Unfortunately, scammers get more and more creative about how they operate, which is why you need to be careful. Below you will find some of the main online scams to avoid.

1. Paying with a Wire Transfer

You will be left open to an online scam if you pay for a product through a bank deposit or wire transfer. Currently, the only way to pay on an online auction site safely is with PayPal, or another escrow-type service. Or, you can pay safely with cash when you collect the item.

2. Fraudulent PayPal Account

This happens when you have sold an item and you receive an email notification from what you believe is PayPal informing you that your buyer has successfully paid for the item. You are pleased and mail out the item, but then you check your account and realize you have been scammed. It was a fake email that looked very similar to the usual PayPal notification. Always look at your PayPal account first, so you can see if the buyer has paid the money.

3. Timeshare Cancellation Scams

Generally speaking, any service group claiming that they can cancel your timeshare is usually a scam. You have a window of time to cancel a timeshare legally; when you pass that time, cancellation is not possible. Many timeshare cancellation companies, like Mexican Timeshare Solutions, will tell you that your timeshare has been cancelled, but when you contact the resort directly, you will find your membership is still registered and accruing debt.

4. Hijacking Someone Else’s Listing

This happens when you have purchased a high-dollar item like an expensive car or computer, but the seller persuades you to make the payment outside of eBay. When you go to get your item, the actual owner informs you that the car has never been listed on eBay. The seller had hijacked a listing from another site, pretended to be the owner, and now vanished with your money.

5. Postage Scam

Anytime you sell an item that requires shipping costs, an online scam can occur. The buyer pays for postage for the item and then later contacts you personally by telephone to say that they would prefer to collect it in person and have you refund the cost of postage in cash. A few days later, you receive a complaint from eBay and PayPal claiming the product wasn’t sent (which it wasn’t because they collected it) but you can’t provide any proof that the item was picked up. You are forced to refund the entire purchase, including the shipping costs!

6. Purchasing a Picture

One of the most disheartening online scams out there, especially on eBay, is when a seller posts a high-demand product such as a PlayStation One, Xbox One, or even a MacBook. You win the auction, so you pay for the item. The buyer sends you a photograph in a frame claiming that you ‘technically’ paid for the picture. Usually these scams are easy to detect because the low cost of the item is too good to be true.

These are just some online scams to avoid.
Reference: http://www.welivesecurity.com/2015/02/09/common-ebay-scams-avoid/