I buy all my electronics from Amazon with the exception of motherboards, because of their hassle free return policy. I normally buy my MB's from a retailer so I can see/control what board rev I am getting. If there is only one version, I use Amazon. Gig boards do come with a single piece of tape like dmdilks mentions. Box is not sealed.
Amazon doesn't sell used equipment. Always select ships from and sold by Amazon, LLC. If you bought from a 3rd party in their marketplace, you are taking a risk. The equipment I've purchased directly from Amazon has always been new, and you can't beat their return policy.