I run a classified site and have different opinion:

• Submit your individual classified listing pages to site map. Title and descriptions of each classifieds are different and can help you bring long-tail traffic.
• Submit your individual classified listing images in site map, it will help you bring traffic through image search.
• Google and everyone else strong recommends to use rel=next and rel=prev rather then putting canonical to the first page. Also don't use both of them together because you will be confusing google. If you have to put canonical then do a canonical to the page minus anyother sort parameters so canonical on page 2 will be pointing to page minus all sort parameters, etc.

Hope it helps !

Although Google and Bing have recommended that the same URL be used for serving desktop and mobile websites, portals like airbnb are using different URLS to serve mobile and web users.

Does anyone know why this is being done even though it is not GOOD for SEO?

Hi HaCos,

Well it depends on how many users are there? thousands of users with thousands of sub domains is an expensive option. Go for user subdirectories instead of sub domains. And as each user got a sub domain too, so make that sub domain canonical of user sub directory. Hope this answers your question.