guidestones have 2 possible places,
also its possible someone just before you took it, it needs some time to "respawn"
ofc doing it by marks of fate is more timeconservative, but i guess you play the 1st time, in his case i would also do this quest, simply because its good to better know that map
lol @ the hiden ad of the goldspammer

you can block him by rightclicking him and select ignore