This scenario is inspired from the KP of last week.

End of turn of Norbert's turn, Albert fetches for a land. He shuffles his deck and does not present it to his opponent. Albert then directly untap and draws his card for the turn. Norbert calls for a judge.
After investigation, you believe Albert did not cheat (by shuffle tutoring for example). The card drawn cannot be identified in Albert's hand.

What would you rule?
Would you rule a DEC, apply a Thoughtseize, shuffle, and then let Albert draw a card for the turn? Would you give an IS and just shuffle the rest of Albert's library?

So first things first: what would be our policy justification for DEC? The cards in his hand are there legally. The root infraction is Insufficient Shuffling. Suppose you saw a player draw a card after pile shuffling once, then presenting to the opponent who gave a single cut; would you rule DEC there as well?

Regardless, in the scenario you've described, I think the game state is fine as is. Assuming that Albert shuffled well, a random deck is random. The opponent shuffling the deck doesn't make it “more random” than it was; it's just a safeguard against cheating. The warning is appropriate to educate the player about proper procedures and to track this behavior unless it recurs. But nothing about the game state is sufficiently damaged that it requires a fix, aside from properly shuffling the library.

It's only TE - Insufficient Shuffling if the player doesn't sufficiently shuffle their deck after searching for a card. I wouldn't classify forgetting to ask the opponent to shuffle/cut falls under this. To me it feels more like something you'd remind the player to do.

Originally posted by Mark Brown:

It's only TE - Insufficient Shuffling if the player doesn't sufficiently shuffle their deck after searching for a card. I wouldn't classify forgetting to ask the opponent to shuffle/cut falls under this. To me it feels more like something you'd remind the player to do.

While normally I would agree, the most recent MIPG contained an update to the definition for Tournament Error–Insufficient Shuffling and now includes the following…

A player unintentionally fails to sufficiently shuffle his or her deck or portion of his or her deck before presenting it to his or her opponent or fails to present it to his or her opponent for further randomization.

…and as the scenario describes that the player failed to present his or her deck to the opponent, the infraction was committed.

Now, if the player presents and the opponent simply chooses to do nothing, I would agree that no infraction has been committed. But I would gently remind the opponent that because this is Competitive REL, they are required to shuffle.