Step 1: Search and find the product on and take a look at the web page address

Step 2: The number you see at the end of the website address is the Product ID. 

For example, 413344702  is the Product ID for the item:  

TIP: Rather than using the Product ID on Sellegr8, you can also copy the entire URL of the product and paste it into the relevant text box in Sellegr8. Sellegr8 will then extract the Product ID for you and will use it instead of the long URL.