It heavily depends on the author's distribution method. If the author is personally sending you a dm and giving a link with just one single card?
80% chance of it being marked. But it also depends on whether you are a new or a regular client, if he trust you or not.
The more the author tries to hand things to you personally, the more likely it is to get a real mark. Because a guy like Suou wants to know everything about you first before handing the stuff the you brought, he is very strict with people.
But a guy like Sunset Rayline may says he marks his stuff, but the truth is that he just changes the MEGA link every once in a while, so Kemono doesn't get to be useful against him.
Anyway, there are still a lot of ways to be safe against this. If it´s a patreon shop, gumroad or payhip: You can use a 24-hour temporary card and share stuff without fear. Have alternative discord accounts, alternative patreon accounts. Be smart about how you buy stuff on the internet.
Some old posts that Imai-sensei made here are still also very much worth reading:
Koikatsu card sharing request thread. コイカツ koikatu!
kk.now.cc
And a updated list now would be:
Character: AOMI, MogelatteRio (RiOAXERᐃLixX), Suou, Dolores, Keiyuu (Patreon), Himiko (Patreon), Yimeng, LDKI and Unagi4545.
Leakable: Dolores (Patreon shop), Himiko (Patreon shop) and Keiyuu (Gumroad)
ONLY if you use a 24-hour temporary card.
Inactive: ANT-Y and H-Axiom are dead. Xcalibur, WammonTusk and Cetol are missing since January, April and May.
I also want to warn you to not to trust people on this forum too much, even the veterans here have made mistakes about whom to trust.
For example, Imai-sensei once recommended someone here to me if I want to ''unmark'' cards, but looking at that person history post now, it became very clear in that last fight that he is affiliated and loyal to Earthship. So yeah, almost made a mistake, don't dm or accept dms from people and don't believe in miracles about this stuff. Also, if you have marked stuff, don´t say what you got publicly, it just gonna be a headache to you.