People who send cold invites should be reported as annoying other users, the report options should include “this person is pestering/annoying me”. its doubtful those who send cold invites are doing it just to one person, so if someone's reported multiple times over a short period they should recieve a warning and if they keep doing it, are disciplined like an abusive user would be.
(I'm saying this based on the assumption that the option isn't already available, if it is people should use it and Achat should enforce it)
There is only so much the Development team can do at once, so we as users should enforce it ourselves as well by asking cold inviter's to stop, or by ignoring them.