Online auction is a popular electronic marketplace that allows buyers and sellers to purchase and sell products in an efficient way. In spite of popularity of online auctions, there are many fraudulent bidding or selling behaviours that can occur during an auction (e.g., shill bidding, bid shielding, etc.). Among auction frauds, shill bidding is one of the hardest types of auction fraud to detect. Researchers have developed fraud detection and prevention methods for combating such fraud. However, it is difficult to effectively identify and recognise bidding behaviours for detecting shill bidders in online auctions. This paper presents a brief overview of major research on bidding patterns for detecting shill bidders in online auctions. Moreover, our analysis result illustrates the characteristics of such bidding patterns represent strong signs of shill bidding when monitoring online auctions to combat this fraud. We also present case studies for identifying shill bidding behaviours in the datasets of eBay.