ShelfKeepr scans eBay and Etsy throughout the day for the books on your want list - first editions, out-of-print runs, the one volume missing from a set - and emails you the moment a copy turns up at your price.
Hello Product Hunt, I'm Jamie. The creator of Shelfkeepr.
It came from my own book buying. The copies were out there, but checking eBay by hand every few days meant I either missed the good listings or paid over the odds because I couldn't wait any longer. I'd also bought the wrong edition more than once.
ShelfKeepr does the checking for you. You add the books you're after and set a maximum price. It then searches eBay (UK, US, Canada and Germany) and Etsy through the day, and emails you when a listing matches. It also looks for cheaper editions of the same book, because the edition you'd have settled for is often a fraction of the price of the one you searched for. (More marketplaces coming soon)
The approach changed quite a bit during the beta. I started with one narrow corner of the book market, then opened it up to any book once it was clear the problem wasn't specific to one genre. Beta members told me early on that most of the difficulty is matching, not searching: telling the right edition apart from a prequel with a similar title, or a paperback from a collector's hardback. Most of my time since has gone into that.
I'd really like to hear what doesn't work for you, especially if it matches the wrong book. That's the part I'm still improving.