18 U.S.C. § 371 : US Code - Section 371
"If two or more persons conspire either to commit any offense
against the United States, or to defraud the United States, or any
agency thereof in any manner or for any purpose, and one or more of
such persons do any act to effect the object of the conspiracy,
each shall be fined under this title or imprisoned not more than
five years, or both."
I've bolded and underlined the portions that matter. I agree that selling an iPad would not count as "an act to effect the object of the conspiracy." A conspiracy can be punishable whether or not the agreed-upon offense ever occurred, but the sole act to effect the object of the conspiracy, selling an iPad, is legal.