Have never "sold" records or sheet music - however, the net, and lists, and the "find-feature" are a quick way to check valuations, if for only curiosity's sake....Its nice to see a "favorite piece" valued by someone at $50.00. However, when it comes time to sell - expect 10 cents on the dollar, selling to a wholeseller. (For U.S.tax purposes, value of a donation to a "charitable organization" may be set at the value the organization could sell it for - this is better than 10 cents on the dollar, if you have a taxable level of income.)
For valuation of folk vinyl - here is list where you could start your research.