A link would be useful so we could see what you're talking about.
Truthfully, as a rule, the wire on Amazon may not be the best quality. I bought THNN wire from Home Depot, at the time it was like $44 for 500 feet of # 12 pure copper wire. You do NOT want CCA (Copper Coated Aluminum), it doesn't solder well, and it's not as good a conductor either.