Many of the agents we work with manage properties where the landlord is happy to accept tenants using DSS or Housing Benefit.
Unfortunately, there is no blanket rule to apply as it is down to the individual landlord to decide whether they are willing to accept DSS tenants.
With this in mind, if you find a property you are interested in on Facebook Marketplace, the best thing to do is to send an enquiry using the "Contact" or "Request Viewing" buttons and include in your message any details of your Housing Benefit situation. By including this information in your first message to the agent you will not waste any time arranging viewings for a property where the landlord will not accept Housing Benefit.
It's always a good idea to explain a bit about your situation and highlight your reliability as a good tenant to show the landlord or agent that you will be a great fit for the tenancy.