This sounds a lot like "spiffs" that are paid to employees of car dealerships (or at least they used to be, I don't have any clients in that line of work anymore).  

You can do an online search and find different answers.  Here's one from NATP that says, for the facts given, it's not subject to SE tax.  

https://blog.natptax.com/article?articleId=6SoZF5qEZaPVJ5fWKKKRM8

Reminds me of the Big Pharma sales reps who delivered free pizzas to the nurses in clinics that used their products.  (FDA rules have since banned much of this.)  And of course tonight we have the Oscars, and the question of whether the "goodie bags" are taxable.  But SE income?  I vote no.