I never get guild marks for the class I'm actually doing leves as. Never. It's random to so you can forget planning on getting guild marks when you need them. It's a completely assinine system they thought the players wanted- no, NEEDED, as a way to progress your character. Random chance of a random number of guild marks on a random class you have up to the eligible level. I think my chances are better at the slots in the casino.
If you're talking about DoW/M then all you need to do is to read the leve or the warning on it and change your class to the appropriate one or just not take the leve.
On DoH/L is impossible to get marks for a different class than the one you are attempting the leve as.
What you're saying is they want me to play on whatever class the freaking leve tells me to play on or gtfo. That's what I mean by asinine. I want to level GLA, thats what I decide I'm going to do when I log in. Why the **** should I have to switch to another class just to get guild marks I don't need. You lose them too if you didn't go and switch classes like a good boy. Who needs character progression, right?
It's just a stupid system and I hope they see how absurd it is at some point, but I'm not going to hold my breath for it. There's better ways to do it but it's so far past their radar it'll probably be in there until the servers shut down (either a year or 20 years from now).