Do you mean you get different search results when you look for things on eBay, depending on which device you're using? That's pretty common. eBay has a search algorithm that will adjust search results according to your previous behaviour on the site which will generally vary between two devices (eg on one, you may have looked for a DVD and bought the cheapest available with free post, so eBay will consider those preferences). In some cases they will use that history to make listings they think are less relevant basically invisible to you, other times they just show a selection in search results, too (if they do this, there should be a small link somewhere on the page that says "view all results" or similar).
If you mean third party advertising, it's actually a fairly similar concept - the ads you see are usually based on your search and browse history, which would most likely be at least a little different between two different devices. eg A couple of weeks ago I bought some new shoes and an umbrella on my PC, so now on eBay I keep seeing ads for shoes and umbrellas (too late, eBay 
). On my phone I'm more likely to see... I dunno, weather stations maybe, since I use my phone to check the forecast fairly often 
