Well, I wouldn't mind having a blacklist, but everyone makes mistakes now and then. I mean, one can be an excellent trader, and then, accidentally, a hacked Pokemon comes under radar. I mean, if it's not intentional, then I understand and one shouldn't be blacklisted for that.
However, if one is intentionally scamming members by trading hacked Pokemon repeatedly, then yes, it's a bad thing.
On that note, it's also possible for one to merely lie about whether or not they knew a Pokemon was hacked or not. So.. yeah D:
However, I don't think that a person's reputation from another forum should carry over - that was there, this is here. Sure, there's a possibility that they could do it here, but there's also a chance they've changed. ):
Hmm. What do you guys think? :)
Edit to Add: And guys, keep in mind, PC is PC. It's not BMGf, SPPf, or Smogon. :)