I remember the designer leather jacket scam, several times being offered "designer" leather jackets in the South Mimms carpark, with the seller spinning a story that this was excess stock from an exhibition he had just attended. Closer examination of the jackets showed they were cheap knock offs worth a fraction of his asking price.
As to this business with the watches - it does sound like an attempted scam, probably shells of watches. If a deal seems too good to be true, and there is a time pressure put on the transaction, almost certainly a attempt to deprive you of your hard earned cash ;)