Assuming the matter went to court, a judget would look to the substance of the transaction to determine what was being sold.

The law does not recognize legal fiction of selling a "white envelope" as it is clear that the consideration paid (e.g. $1000) is not for the envelope but what is contained therein. Similarly, an auction for your "time" spent at the airport would be considered a legal fiction since the buyer is paying for the free ticket not for your time.

People sell white envelopes all the time on ebay but it won't make any difference if they get caught selling - at least from a legal perspective.