My local Oxfam now use the Record Collector price guide book and price even scratched records at Mint prices. Still, some records and CD's are priced cheaply. I recently bought a George Michael promotional CD for £1 and immediately sold it in Discogs for £35 I also bought 22 early 70's Bollywood soundtrack records in perfect condition for 50p each. I know nothing about this genre but they looked new and the sleeves were nice and colourful. Sold most of them for around £12-£15 each.