LinkedIn keeps adding useful functionality. Rolling out today is the Promotions tab within Groups. Similar to the Jobs tab which allows for employment related posts to be segregated, the Promotions section will allow for the organization of offers made by companies.
Keep your group discussions relevant by empowering your members to move promotional and sales content to the Promotions tab. Like the Jobs area, it defaults as visible but group managers will have full control to change settings.
By defining the rules and guidelines for participation within the group rules area, the overall experience should improve allowing people to filter.