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If you deal with a single trading partner – say you sell digital books through Amazon and they have assigned an Amazon identifier to your product, can or should you use that Amazon identifier with Indigo, Kobo, Booksamillion, BN, library wholesalers or distributors? Of course not. The publishing supply chain identifier is an ISBN – that's primary identifier used in B2B publishing data exchange. But that is one of your options: If you only sell through a single source like Kobo or Amazon you can choose to NOT participate in the wider the supply chain. And if that's your choice then you don't need to do ONIX or work with anyone else – it's a legitimate business decision you can make. You accept the terms and services of that single source and direct your marketing to supporting sales through them. No ISBN is required (one may be required to support legal deposit requirements but you're not using it for business purposes).
If you want to be compatible with the publishing supply chain then you must support ISBNs and support them properly.
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