dlvr.it uses a couple of different options for your publishing depending on the service. Some services will not allow us to send our own content, while others will. This can also depend on your posting style.
Facebook and LinkedIn content
Facebook is one of the platforms that is a little tricky. If we are sending posts to them via shared link (making a clickable image that directs to your link), we are not allowed to select our own content. Facebook will then fill in the content from the Open Graph tags on the page. LinkedIn is similar in this nature.
However, if you are sending your content to Facebook as a Status Update (posting text only with a photo), we are allowed to customize content. In this case, we will publish content from your RSS Feed as the text that we send over.
Twitter and others
Twitter is a platform where dlvr.it is only allowed to publish text with attached photos, unless you have items listed that have Twitter Card tags. For text posts in all services, dlvr.it will use the text from your RSS feed for the title and body options.