Can an opponent shuffle your deck (not just cut it), and are they allowed to look at the cards while doing so?

Ruling: Opponents are allowed to shuffle your deck and can insist on doing so, but they are absolutely not allowed to look at the cards in the deck while shuffling.

Sequence:

• Player shuffles their own deck
• Opponent may shuffle or cut the deck during presentation
• Opponent must not look at any cards while shuffling
• If opponent appears to be looking at cards, call a judge

Nuances:

• Looking at secret information during shuffling can result in a warning for violation of secret information rules
• Players should look away (at ceiling) or watch their opponent shuffle to avoid any appearance of looking at cards
• Shuffling the deck vertically where card faces are visible is suspicious behavior
• Pile shuffling can be used to count cards but is not sufficient randomization on its own
• Players appear to be allowed to count opponent's deck during presentation to verify legality
• If you suspect improper shuffling or deck illegality, call a judge rather than handling it yourself