Personally I like bricks and mortar model shops - I bought a lot of 2/hand stuff from the old Bradford Model place in Manchester, an inexpensive way to experiment with kit bashing. Not many model shops bother with 2nd hand these days but I get the feeling that buying via E-bay is more expensive, not least because of the work required on the part of the seller. I haven't bought anything 2nd hand on-line because I cannot examine it. Recently found a shop (Saturdays ony) in Weveram that does a lot of 2nd hand stuff, they will be getting some business from me even though its a fair trail to get there on public transport. On line retailers tend not to engage in lengthy chats about the pros and cons of individual items, they are (in the main) just box shifters, fine for designer tat but not so good when talking about any kind of equipment. I have been helping a chap build a layout of late and the above shop has given him good service and advice, they could have ripped him off but did not do so. Buying 'blind' on the interweb might be okay for 'collectors' but if the thing actualy has to work then bricks and mortar is the way to go.
Regards
Mike