NO !! 
Honestly - it's a minefield. You always get people that really don't understand how this works and can be very disillusioned when they don't achieve "what the guide says". 'Average' to you can be 'Mint' to another person - everyone sees things differently - some rather astonishingly so!! We also have age to take into consideration. There are also fluctuations in prices (monthly sometimes) which would put the valuations out - and supply is always a factor. Lots of products on ebay drives prices down - but if yours is the only one it can make double what the last one did on occasion.
I'm happy to answer any used product questions, and will happily email back members with requests for current and accurate valuations. I do it every day at LifeStyle. Graham will have a good idea too, as will pretty much any of the mod team!
However, if we all feel there is a pressing need for this on site - i will do a guide - but it will need constant, and i do mean constant updating.
Lee
BeoWorld - Everything Bang & Olufsen