A warning system is/was useless for the spambots that copy/paste, use text spinners and used homograph attacks (this last one is no longer possible). For decent real users on the other hand who made a mistake a long time ago, I'm all for less severe punishment.
I can't find a ban list
See
LIST: Banned users (updated once a day),
BPIP (updated continuously), or
modlog (only for the past 7 days).
He's banned:
I suspect if it is real it could be this post .. and it was flagged for plagarism which to me is clearly not his intent.
He does clearly state he is the escrow for the sale
He (or you) can open a ban appeal topic in Meta, if this is the reason it doesn't look like it deserves a ban.