The 90 days grace period is in their Eula because it is the law in many countries, not because Wallmart is cool.
Btw, thus is pretty dumb discussion. If buyer wants to return it, seller shouldn’t care about as long as the buyer is not a pirate. Can’t tell for sure who is pirate or not so you are obligated to act like nobody is.
Acting and enforcing eulas that assume everyone is a pirate won’t do any good to your sales.
The only thing I always ask is for people do not pirate products I put effort into. If they have no use for it, who am I to force them to keep it…