When do you need a GS1 number?
When the barcode identifies a product for sale through a retailer or most marketplaces. Amazon, eBay (for most categories), Walmart, and physical retail stores expect a UPC-A or EAN-13 that traces back to a GS1-registered manufacturer prefix. List a product with a barcode from a made-up or previously cheap resold number, and the listing can be suspended or rejected once the mismatch is caught.
When don’t you need one?
Whenever the barcode never leaves your own systems. Internal stock tracking, warehouse bin locations, asset tags, library systems, and shipping labels between your own facilities don’t require GS1 registration. Pick any consistent numbering scheme and use Code 128 or Code 39, which have no retail registration tied to them at all.
Can you buy a single GS1 number cheaply from a reseller?
You can, but major marketplaces increasingly check against GS1’s own database and reject numbers that don’t trace back to your business. A resold or “shared” UPC that isn’t registered to you under your own GS1 company prefix is a common reason for listings to fail verification later, even after being accepted initially. Registering directly through GS1 is the only way to guarantee the number is unambiguously yours.