I think it's totally justified to leave a negative trust it's been known for the accounts to be sold and then later use that reputation to scam. I think people selling accounts with positive trust are the ones to really look out for though.
And this is exactly what op has done.
I repeat again, this is a question for clearing to every bitcointalk users that trading their accounts is legal or illegal and do not concern mine in anyway!
You sure about that. I remember you being caught and reported for farming a load of accounts in the 777 giveaway thread using bots a while back. Looking at them now many look to have negative feedback and have been shilling for crapcoin ICOs:
https://bitcointalksearch.org/user/twisto-455033 Twisto February 23, 2015, 03:36:01 AM
https://bitcointalksearch.org/user/bitloard-455031 BitLoard February 23, 2015, 03:34:32 AM
https://bitcointalksearch.org/user/silverstar-457072 Silverstar February 24, 2015, 12:52:54 PM
https://bitcointalksearch.org/user/bombding-492173 bombding March 24, 2015, 07:15:30 PM
https://bitcointalksearch.org/user/givedusty-492177 givedusty March 24, 2015, 07:20:29 PM
https://bitcointalksearch.org/user/jimpix-492178 jimpix March 24, 2015, 07:21:26 PM
https://bitcointalksearch.org/user/nelifur-492180 NeliFur March 24, 2015, 07:22:39 PM
https://bitcointalksearch.org/user/needsmorejpeg-506784 NeedsMoreJPEG April 16, 2015, 09:00:53 PM
https://bitcointalksearch.org/user/holybananas-506785 HolyBananas April 16, 2015, 09:01:50 PM
https://bitcointalksearch.org/user/mrlucas-454846 MrLucas February 23, 2015, 12:46:29 AM
https://bitcointalksearch.org/user/danielth-454844 Daniel_Th February 23, 2015, 12:45:27 AM
https://bitcointalksearch.org/user/waterpilem-454839 waterpilem February 23, 2015, 12:42:01 AM
https://bitcointalksearch.org/user/abrahamlinco-454843 AbrahamLinco February 23, 2015, 12:44:41 AM
https://bitcointalksearch.org/user/kamale-454852 kamale February 23, 2015, 12:51:53 AM
https://bitcointalksearch.org/user/th3program-455600 Th3Program February 23, 2015, 01:01:10 PM
https://bitcointalksearch.org/user/elmedorator-455601 ElmedoRator February 23, 2015, 01:01:56 PM
https://bitcointalksearch.org/user/egyking-455604 EgyKing February 23, 2015, 01:02:43 PM
https://bitcointalksearch.org/user/seneor-455612 SeNeor February 23, 2015, 01:16:53 PM
https://bitcointalksearch.org/user/gladucame-455613 GladuCame February 23, 2015, 01:17:45 PM
https://bitcointalksearch.org/user/talkingbad-455614 TalkinGbad February 23, 2015, 01:19:12 PM
https://bitcointalksearch.org/user/dontstop-455615 DonTsTop February 23, 2015, 01:20:14 PM
https://bitcointalksearch.org/user/whynot-455618 WhyNot? February 23, 2015, 01:21:05 PM
https://bitcointalksearch.org/user/joebriggs-492171 JoeBriggs March 24, 2015, 07:13:03 PM
https://bitcointalksearch.org/user/hobbitmud-492172 HobbitMud March 24, 2015, 07:13:56 PM
https://bitcointalksearch.org/user/bitkonquer-457081 BitKonquer February 24, 2015, 12:58:42 PM
https://bitcointalksearch.org/user/supersnic-457089 SuperSnic February 24, 2015, 01:03:25 PM
https://bitcointalksearch.org/user/tankguard-457159 TankGuard February 24, 2015, 02:14:58 PM
https://bitcointalksearch.org/user/darkloard-457164 $Darkloard$ February 24, 2015, 02:17:44 PM
https://bitcointalksearch.org/user/topgun-457167 TopGun February 24, 2015, 02:19:24 PM
https://bitcointalksearch.org/user/nightdream-455038 NightDream February 23, 2015, 03:39:39 AM
https://bitcointalksearch.org/user/theeboss-455041 TheeBoss February 23, 2015, 03:40:40 AM
https://bitcointalksearch.org/user/th3developer-455044 Th3developer February 23, 2015, 03:42:25 AM
https://bitcointalksearch.org/user/the3max-455047 The3max February 23, 2015, 03:43:18 AM
https://bitcointalksearch.org/user/jetpower-455048 Jetpower February 23, 2015, 03:44:35 AM
https://bitcointalksearch.org/user/iilustor-455049 IIlustor February 23, 2015, 03:45:21 AM
So, are you the scammer or are you just selling accounts to them? And no, it's not against the rules to sell accounts, but this is exactly why it's frowned upon.