Donation offered to non profit 510c3: 75 Hard bound National Geographic Books for sale Vol 1 1888 to Vol 97. Missing Vol 5, Vol 9-13, Vol 15, Vol79-87
It looks like you have an awesome and quite large and cumbersome collection of National Geographics. Are they all bound into volumes or are there individual issues?
As others have mentioned you'd make the most selling the collection piecemeal through something like eBay. The newer ones will not command much of a price, but the older ones, even the reprints, are pretty valuable.
Selling them piecemeal on eBay will take some time as you don't want to list everything at once and you'll want to approach the price point from above so to speak by listing them with a high reserve and/or a high buy it now price to determine the market. And drop the price at each relisting until you get it sold.
Less return, but faster, is identifying a high end antiquarian bookseller that specializes in National Geographic magazines and sell them on consignment. They will take a hefty chunk, but they also most likely have a customer list they could solicit.
That said, if you do decide to sell them individually, I am looking for Vol 9 issue 10 - October 1898. Reprint or otherwise.
The least return is selling it outright to the same high end booksellers.
Are those of the first 18 volumes original or reprints?
Pictures tell a thousand words...
Volumes 1888 to 1907 are red cover reprints, volumes 1914 on are original.