There is a seller I came across and I'm thinking about blackmailing them.
Why in the world would you blackmail them?
I think he should be more generous.
Regardless of what you want from them blackmail is wrong. You could get in legal trouble for blackmailing someone.
It's just a minor scam, I should be fine.
Blackmail is wrong and it's certainly not minor. If you don't think the seller is not generous enough then you should take your business elsewhere. Blackmail is illegal, doesn't that worry you?