to question whether or not the OE Nissan parts are legitimate and decide not to purchase anything from him. He's now tainted his integrity to a very large customer base. IMO, it would be foolish to limit yourself to thinking that the so-called "smaller" manufacturers are the only ones at risk - it wouldn't be all that hard to copy other items (i.e. Nissan OE parts) as well.
You're also dismissing other customers who will bypass/boycott patronizing him solely out of principle. I'd wager that this will take a significant chunk out of his business.
Most of all, tt.net is worse than a group of pachyderms when it comes to remembering things - especially when it's something of this magnitude. This will live on for a very long time.