Originally posted by Darren Horve:

Can't check right now, but arent you supposed to sleeve your Tokens in a differently than your 75? Or is that just a really good 'suggestion'?

Tokens must not appear similar to the sleeves of a player's deck (MTR 3.8).

I also suggest that players not sleeve their sideboard, instead exchanging sleeves when they exchange cards. This is to reduce the chance that a sideboard card will have a sleeve much less worn than the sleeves on main deck cards and therefore turn out to be marked. This suggestion has not gained much traction due to inconvenience of swapping sleeves and some players' desires to be secretive about how many cards they are sideboarding.

There are many sleeves that become damaged more easily when cards are moved
into and out of them, particularly the way that many players pinch the top
of the sleeve and slide it between their fingers to create a spaces to
insert the card. I personally always shuffle my sideboard into my deck and
remove 15 cards as a personal preference, but that's neither here nor there.

I am confused. The OP, as I recall, gave us that the player stated he
would admit he had no sideboard if asked to present one. Why are we
arguing about the confusion of the sideboard presentation? “I don't have
one” seems to be fairly unambiguous and unlikely to lead to confusion about
whether the cards he's messing with between games are part of his sideboard
or not. If the opponent chooses not to inquire and assume that he is
sideboarding, that is the opponent's choice.

I am curious: how many times have you seen sideboards presented? It's not
all that often. I am not even great myself about making a point to do
this. I expect that is this player's gamble, and he's admitted that the
jig will be up if his opponent asks about it. I am not sure what the
problem we have here is.

There was a recent Knowledge Pool, regarding a token mixed in with a player's deck. I don't see why this situation is any different. Blank cards, tokens, etc, are not Magic Cards, so there is no rule about them being allowed in a player's deckbox allong with a sideboard. I don't think there's any infraction here.

I would suggest that a sideboard of 15 basic lands is a better idea in the future, since that removes any suggestion of cheating.

I wouldn't give the player an infraction for this, but I would advise the 15 Island sideboard in the future.

Specifically Islands because of all basic lands Islands have the best win percentage (I believe it's actually a documented fact that “Island, go” has the highest auto-scoop percentage of any “basic land, go” opening play in Magic)