I'd say the exchange with Ted Raimi ("Did you say the words right this time?" "Well, maybe I didn't say every tiny little syllable, no, but basically I said 'em, yeah! Basically...") is meant to indicate that not saying the words right is what causes the S-Mart Deadite.

As for the worthiness factor, the parents tried to give the item back, not the boy, and either way, I think the idea is that you would suffer for three days regardless, and at the end, you would be judged. Of all things, the option to give the item away seems like a pretty massive test; if you shamefully accept your fate, you've clearly felt remorse, but if you try to shirk it off onto someone else, no matter how deserving they are, you're passing the buck.