Stealth is essential as trolls love to eat muggles, who tend to just blunder about unaware of such beings. If you approach quietly, so as not to disturb them then they are not likely to be annoyed.
Good manners, well, I'm sure you are good mannered anyway, but you have to remember that it is Troll manners that really count here. So, don't go shining torches at them, they hate the light as it gets them stoned! Take a small gift for them, they love hoarding stuff and if they have something shiny and new to look at they will soon forget about you. If you can, play some music by the Troggs (some say they are related somehow).
The cache is a small screwcap tube with a pencil.
Congratulations to Skippy and Pingu and the Molecachers on being joint FTF.