A house cannot be blacklisted - there is no such thing.
When a credit search is done, it is the individual (and any known associated people who share a financial link) who are searched.
When your son was told he was refused credit he should have been given a leaflet which told him of the company used to obtain the credit search.
As mentioned above, google each of the companies mentioned and get a copy of your report (statutory copies cost �2.00) - this will throw some light on the situation