I contacted this guy on Skype, he sent me a screenshot of his backpack full of TCG mounts that could easily of been faked and said he could not prove he had a working dupe method "in case it gave away how to do it". I'll post below the conversation that took place on Skype and leave you guys to make your own mind up.
[22:16:32] Ali Ünlü: Hello
[22:16:43] gh1981: hey
[22:16:59] gh1981: so. you are selling this dupe method?
[22:17:15] gh1981: explain to me which dupe you are selling, i don't want one involving a GM
[22:17:17] Ali Ünlü: Yeah indeed, however I've sold it to 2 other people just so u know, not planning on selling it to more then 3 people.
[22:17:40] Ali Ünlü: I can't tell you how the dupe works, it's a unique method that's one of the most recent ones, as me and my friend found it when messing with the Fuse Exploit.
[22:17:46] Ali Ünlü: It has nothing to do with Game Masters etc
[22:17:51] gh1981: ok...
[22:17:54] Ali Ünlü: And it can not be used to dupe gold, it only works with items.
[22:18:13] gh1981: ok
[22:18:20] gh1981: how can you prove to me you have a working method?
[22:18:37] Ali Ünlü: well I could send you a picture of my backpack, and prove that the char in the Ss is mine
[22:18:39] *** Ali Ünlü sent dupe.jpg ***
[22:19:17] gh1981: Ill be honest
[22:19:27] gh1981: Ive spoke to 3 or 4 people who claim they know a dupe on ownedcore
[22:19:44] Ali Ünlü: yea?
[22:19:48] gh1981: only 1 of those people actually proved he had a working method cause he could share his screen and show me him partly doing it
[22:19:58] Ali Ünlü: I'm sorry, I can't do that.
[22:20:08] gh1981: I know some of the ways this dupe works
[22:20:11] gh1981: but not all
[22:20:34] gh1981: how much are you asking for the method?
[22:20:41] Ali Ünlü: 65$
[22:20:49] gh1981: whats ur char's name?
[22:20:53] gh1981: so i can armory it
[22:20:59] Ali Ünlü: Emphatize
[22:21:02] gh1981: realm?
[22:21:05] Ali Ünlü: Auchindoun
[22:21:09] Ali Ünlü: EU
[22:22:34] gh1981: ok...
[22:22:41] gh1981: no spectral tiger on your main
[22:22:46] gh1981: even though you can dupe them...
[22:22:54] Ali Ünlü: I haven't used any, I'm selling them so
[22:23:22] gh1981: so you cant prove you know a dupe
[22:23:27] gh1981: all you have is a screenshot
[22:23:37] gh1981: and you want me to give you $65...based on a screenshot?
[22:24:05] Ali Ünlü: You don't have to, what I'm doing is, I'm trying to earn real money on a dupe that I've found
[22:24:13] Ali Ünlü: Ur not the only one that is interested so
[22:24:21] gh1981: I understand
[22:24:36] gh1981: but im just trying to establish something
[22:24:40] gh1981: obviously I dont wanna get scammed
[22:24:48] Ali Ünlü: There is noone who wants to get scammed...
[22:25:06] gh1981: so what can you do to prove you have a dupe method?
[22:25:24] Ali Ünlü: Not much, as I could risk showing you it without doing that on purpsoe
[22:25:46] gh1981: ok tell me a few little bits about how its sort of done
[22:25:52] gh1981: leave out the important bits
[22:25:54] gh1981: obviously
[22:26:09] gh1981: cause I sort of know how its done anyway, this way I'll know if you're lying to me
[22:26:10] Ali Ünlü: give me a few minutes, must talk to a friend
[22:26:17] gh1981: sure thats cool
[22:33:10] gh1981: you spoke to him yet?
[22:37:25] gh1981: hello?
[23:09:49] gh1981: no reply dude?
at this point I gave up and figured he's just another person trying to scam, but obviously you guys can make your own mind up