I went on the wednesday, and I know he had sold a couple by the end of the day. But I saw 32 pattern yellow mae wests from £200 up to £400. I found little to be had myself, which has been the case for three years running now.
As for your other point - money! If you can make something for £50 knowing it'll make £200, thats your answer! One good example was the repro Mk IIs that arrived some years back. Basically driving goggles, in a tin, lovely paper label on the tin, large AM stamp on the label and goggle srtap and rust spots on the tin. All rubbish but they still fool people because of the authentic looking packing.
Bargains, unfortunately, come up less likely than they seem!