I have bought at venues, Keith Williams has always been a good place to visit and wherever he is I'll go see. Having said that I've come to the conclusion that the majority of records are at the top end of the price range, VG-ish condition and nothing that tickles my fancy. There are the exception, I thought that the sellers at Cleethorpes last year were very good and I did buy some but at the smaller venues it tends to be the low end stuff.
I do buy on Ebay, you can still get a bargain, I try to stick to US sellers though, they tend to be cheaper and the records better condition (although I have to say that when a UK seller says 'Mint' it usually is just that).
I avoid the GEMMS, Musicstack and the likes, over-priced, badly described and no way to get refunded (the mark of a good seller).
Right now this is not a bad place to buy, also I ask people I've known for a while if they are selling anything.
Not sure I'd agree about the reason for lower prices, the NS world is a different place than 5/6 years ago, the real oldies are nudging 60,
the returning soulies have re-bought their collections and with the current economic climate people have other things on their mind.
BTW it is OK for people to buy to DJ I do know a few who do that but they've tended to lose money, not much but lose all the same.
Message : negotiate, negotiate negotiate..........................