Correct, we're not buying salvation with good works. There's no scale where if we perform enough good works we can go about doing evil works. It's not currency, we can't by squat with it.
Try to follow this, we buy grace by keeping the commandments. That's part of a covenant, an agreement that if we do this, He will give us that. We're not buying it, we're confirming to an agreement. But that's for those who have made the covenant. Those who haven't will be judged according to their works and they certainly are buying anything with their good works. But if they are evil, just like evil Christians (and they ought not keep lying to themselves,.that is not an oxymoron. Just look at all the Christians couped up in prison) they won't be able to obtains salvation without paying their own debt. Good luck with that.