If the phone was in a sealed HTC box it was a new unit. Referb units usually are not in a sealed box. The two referbf I've gotten were in a small Verizon box. Also, referbs are usually not packaged with manuals, cables, etc.There is no marking on the phone itself indicating it is a referb that I've ever seen.
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Drop Box referral- Drop Box
Copy Referral - Copy
(extra 5GB by using this link)