If you have, you may have been charged for it.
It appears as a nominal 1p on the bill and customer services assured me that this was a technical requirement and it would not be charged to my card. Guess what - it was.
Obviously this is only 1p (2p in my case as it affected 2 orders) but it is a matter of principle. also, if it was applied to every order that received a "sample" that could amount to a fair amount.
Check your card statement against your tesco.com receipt to check.