Buying via Chrono24 seemed the better way to go, avoiding most of the risk involved in buying a high-value item direct from an unknown seller, possibly overseas. In particular, good to know that money wouldn't be paid out until a watch had arrived and you had a chance to check it was "as advertised". Having a large number of watches to choose from on a single site also really helped to get a feel for what the options are and how much different types of watch typically sell for. Would recommend.