Best online source for music CD's

+1 for Discogs. I purchased a lot of hard to find CDs there. Locally, I shop at Silver Platters and their flagship store in Seattle has a huge selection of new and used CDs, movies, vinyl, and books. You can also buy from their website: www.silverplatters.com

@limomangus 

Yes indeed local thrifts and churches and public library.

Curious as to the condition of CDs you get from such sources. I worked at a library and patrons scratched the heck out of CDs. I’ve never tried thrift stores, as I figure, based on my library experience, that most people are a good deal more casual about handling CDs than I am. I have enough trouble as it is with the variability of online sellers’ CD grading accuracy.   

Knock wood but I never had to make a return with Amazon.  I also use Presto