While subscribed, cartridges are free and you're billed per page. If you could keep the cartridges, canceling would potentially net you many hundreds of extra pages for free. And you could cancel again and again.
I think the incentive to cancel right after receiving a new cartridge would be extremely high, to the point of rendering the whole service non-viable.
HP would have to limit how frequently customers can cancel, institute a waiting period before resubscribing, or track individual abusers and issue lifetime bans.
The first result for genuine HP ink cartridge on amazon is $23, and has a claimed yield of 170 pages. Meanwhile, the cheapest plan for HP instant ink is $0.99/month. If you could subscribe for the cheapest plan, then instantly cancel, you're basically getting a 96% discount on ink cartridges.
That eliminates the risk of any angry customer with disabled ink.
However, the new problem is that most customers would rather have the current situation pay as you go situation than pay up front.
Id be dammed if I pay full price for a product AND a subscription. If it is a 50% discount (as advertised), the customer is still looking at 3 cartridges before they break even.
I think the incentive to cancel right after receiving a new cartridge would be extremely high, to the point of rendering the whole service non-viable.
HP would have to limit how frequently customers can cancel, institute a waiting period before resubscribing, or track individual abusers and issue lifetime bans.