Even when amazon shows that you're on the manufacturer store, it still may not be genuine. I bought an intel wifi card off what looked like the official intel store on amazon, but it turns out that it was an out of production model sold by a third party, but amazon showed that it was "Intel". Very confusing and frustrating if you don't know what to look for beforehand.

Does Best Buy not resell returns?

Yes, they do. Plenty of horror stories on r/datahoarders of fake resealed HDDs.

I once bought a "new" hard drive from Amazon. It was an enterprise datacenter drive with thousands of hours. Someone had scrubbed the SMART statistics, but did not wipe the drive. They deleted the partition table, but it was still chock full of data. Mostly encrypted, but there was plenty of cleartext logs including runtime statistics for the rack the drive was in.

I'm about 85% sure it was a decommissioned Backblaze drive based on the logs I could see. This was probably 10 years ago, though.