Ebay might be ok, you might also look for "factory refurbished" phones of the same model on Amazon or your carrier web site. If you sell it instead of keeping it, your sales price may be an accurate FMV as long as the sale was fair and well-advertised and you sold it to a stranger and not a relative or friend. If it is never-used but has cosmetic damage, that might be a different value than a phone that was used for 6 months before being returned as defective or unwanted. Ultimately the burden of proof is on you to show that the FMV is less than the contest sponsor claimed.
