These badges have been widely faked using fake plaques added onto genuine and fake Cornwall badges. Very often the metals do not match up exposing the fact that the plaque has been added on to at a later date. The badge should pre-date 1908 and I am dubious as to whether sliders were ever correct. I would ask the seller for a picture of the back to judge for yourself whether it is indeed 100 years old before bidding as it is easy for people to get confused when selling things on ebay.
To show the amount of these about a quick trawl on Ebay shows a second cheaper one here:
http://cgi.ebay.co.uk/CORNWALL-LIGHT...1%7C240%3A1318
The seller does not date it and it is described as new.
There is another ''version' which uses an additional scroll added on the botttom which is also seen on Dorsetshire and other Bns.
As to the authenticity of VB badges in general on Ebay, there are several dealers out there who fill their stock lists by buying up the few genuine rare badges that do appear on Ebay - any genuine VB badge would be worth £40-100. The occasional genuine VB badges listed are quickly spotted and sniped by these dealers. If the badge is going for £6 you have to ask yourself why they are not being snapped up and featuring on these dealers' websites.
Alan