That visit from the guy claiming to be from Red Bull Marketing sounds very suspicious to me. The real motive might be to case peoples houses and set them up to be burgled. Although he may have an what appears to be a valid business card an associate of him may carry out the burglary. A report on this site ago said that a con man was going around and one of his ploys was to say he had customers in the area which is what this guy claimed.

Finally if he offering a valuation he must know estate agents do it free of charge.