Travelodge etc. aren't maintaining a black list, where do I start: why would they pay someone for a non-problem, where to put the list, data protection act, bad publicity, sending customers straight to your competitors, legal risk if it leaks out.
Good WGs don't mind booking hotels Anth. Some work exclusively from Hotels. If a WG is willing to book a room I would take it as a good sign that the service will be good based on personal experience, allowing for them having other bookings.