The simplest way to see how much product a competitor has is to use what we call the "999 Trick". There are also various free and paid tools that will give you this data.
999 Trick
First, you have to go to the listing, and then get to the page when you "See All Sellers". Then find the seller you want to check the inventory of, and click Add to Cart next to their name, as if you are purchasing the product. When you're at the next page, you should be able to change the quantity. Change it to 10+ and type in the quantity 999. A message will then appear letting you know how many units this seller has left.
How Many Extension (Free tool)
You can also download the How Many? Chrome Extension. Using the chrome extension, you can see how much inventory every seller on a giver product page has (image below). The free version will allow you to run analysis on 5 listings per day. You can access the extension here: https://howmanyextension.com/ If you choose to pay for the How Many Extension, get $14.95 off your subscription with code: ELMPFU
