Okay, first of all, you don't need a LLC to purchase GS1 codes. You can be a sole proprietor if you wish.
Next, Amazon has threatened to tighten the noose and verify that all UPC codes you use are actually registered through GS1 in your name. They haven't done it yet, but it could happen at any time.
Resellers can sell you use of a code for cheap, but it will always be registered in their name and, therefore, they could be a problem in the future.