@richardmathes there are cheap bar code scanners that can be used with different software products. I used a $20 one for a program called Readerware Music. I found it much easier to scan into a queue and then let the program go find the listing on discogs or amazon, rather than manually enter them in discogs, which still has no bulk upload function as far as I have seen. This program can export as well. This does not guarantee a match though, as imported albums or cds will not always match upc codes and older records ('50's-'70s) generally don't have one but a publisher/label id instead.
I like the idea of selling to a dealer. There are a couple channels on youtube that are store owners that sometimes report "good hauls" and actively buy and sell off collections. But it would still be worth it to leave someone a rough estimate of value if we are talking collections with a built in value, limited audiophile releases and the like or rare pressings that were or became investments. cheers