[mattcaywood]

viaLibri (https://www.vialibri.net/) includes ABEbooks and the other major US marketplaces (Amazon, eBay, Biblio, Alibris) and international marketplaces. It's far more comprehensive than bookfinder4u, which doesn't do well for books published before ISBNs were introduced (~1970).

[wrp]

Thanks, this looks like a good alternative. One thing though is that people may find the presentation of results easier to search through in BookFinder4U. For pre-ISBN books, you need to use the Out-of-print Search. I use it regularly to find old, limited run, academic monographs.