Gmail has the ability to automatically filter email for you.
If you open one of those offer messages and use the three dot menu in the upper right corner, you can choose "Filter messages like this". From there you can set up a filter rule based on sender or title (or both), and have those messages skip the inbox entirely and be sent to a separate folder (or "category" or "label"). Create a label called "eBay" (or "junk") and have your eBay email messages sent there automatically. Just check that label once in a while to make sure that important messages do not get sent there by mistake.
Using such filters can make your inbox much more manageable.
