I don't see the wording as ambiguous. I can see how someone might try to convince someone else that the wording is ambiguous, but the statements of needing to declare the number of cards you will draw before drawing and of any - that's the important word here - drawn beyond that declared number having, specifically, no effect.Good point but the wording is ambiguous, there needs to be additional information e.g the Deck cannot be used by that person ever again.
It's easy enough to rule that once you've drawn your declared number of draws, that Deck will no longer function for you. That's how my table handles it. While we've never gotten our hands on one (the Decks we've encountered have been owned by NPCs who usually let us draw for a price) it might be fun to have the party wandering around with a Deck that no longer functions for them, trying to tempt others into drawing from it.
That's still broken and abusable though. You have to prevent the Deck's owner from offering it to other people. Otherwise you could just e.g. offer it to random peasants until you find several who get Fates cards, and then draw a bunch of cards yourself after paying them to keep you safe from Euryales/Donjon/etc.
Another abuse is offering it to random peasants in exchange for half of the wealth they receive.
That's still broken and abusable though. You have to prevent the Deck's owner from offering it to other people. Otherwise you could just e.g. offer it to random peasants until you find several who get Fates cards, and then draw a bunch of cards yourself after paying them to keep you safe from Euryales/Donjon/etc.
Another abuse is offering it to random peasants in exchange for half of the wealth they receive.
I would go with an in-world solution for any excess or abuse of that kind. A rapidly increasing "chance" of some arbiter of Fate intervening in shutting them down.
Would work it into the world flavor...high magic world an archon would show up and demand the deck, or perhaps a slaadi Death Lord wants the entropt spread and condones this use, with various in game repecussions sycu as the fall of civilization.
Low magic, portents and dreams of a sinister nature foretell repercussions for the abuse. Until one day a mysterious vagabond curses the deck, and flees to an isolated castle somewhere in the dangerous wilderness.
That will bite the PCs in the rear in little time with even a halfway clever DM. The first peasant to draw the Moon might use the Wish(es) to kill the party and take their stuff. A peasant who draws the Sun will suddenly become 9th level and might not feel like sharing (this admittedly wouldn't be an issue for a high level party). A peasant whose friends were killed drawing from the Deck might use Fates to prevent the party from ever having found the Deck in the first place (thereby restoring his friends to life). On top of that, any good-aligned party would be unlikely to use peasants as fodder for such a dangerous item. But even an evil-aligned party should be hesitant about putting that much potential power into someone else's hands.
Meh. Instead of getting into a war of escalation with the players (with me having to invent multiple Slaadi Death Lords out of thin air if they kill the first one), I'd rather just fix the problem at the source and go with the suggestion from earlier of making the Deck lose its magic after the full draw completes. Don't gamble what you can't afford to lose, says I, and that includes "Don't offer something to your players that you're not prepared to let them have."