Rather than 'blackmail', how about "Coercion" and "Theft in the First Degree" for the customer and all the friends as co-conspirators?

Or maybe "Racketeering" under ORS 166.720.  That way everybody would have to pay back the store three times the value of the property illegally obtained.  And they would be jointly and severally liable.

And it is a Class A Felony.  

" (3) It is unlawful for any person employed by, or associated with, any enterprise to conduct or participate, directly or indirectly, in such enterprise through a pattern of racketeering activity or the collection of an unlawful debt."