Agree with Phoebe and Jeff.  First, having an income reported in Box 7 of 1099-MISC does not dictate that the recipient is subject to SE tax.  Question remains as to whether the income is derived from a §162 ToB pursuant to §1402(c).  That is a determination you and your client will need to make based on his/her set of facts and circumstances.

Your client should not be shocked to receive a 1099-MISC.  It was reported that the products sent for review are technically on loan but reviewers are not obliged to return them, hence the money's worth is considered income and 1099-MISC is issued as required when the value exceeds the threshold.  It was also reported that the T&C for Vine participation were updated back in 2015/16 to reflect these changes.

https://en.wikipedia.org/wiki/Amazon_Vine

https://thewirecutter.com/blog/amazon-vine-reviews/