On that aside... Try sending a message.

Code:
/tell Farmer31 Hey, I'm trying to hunt Parasol Mushrooms.  I need five.


And they often will reply

Code:
Farmer31: Oh, I didn't see you!  I'm looking for Rat Tails.


And now you can offer to trade them the rat tails - or even leave the rats - so they can get those, while they can avoid the mushrooms you wanted.

Another is to ask if they're going towards a certain boss.

Code:
/t HighLevel90 Hey, I'm trying to get the Boss in the Green Zone.  What are you trying to farm?
Code:
HighLevel90: I need all the arts
Code:
/r Okay!  I'm collecting any goblin cards under level 24, too.


This doesn't always work, but when there's a high level, well, that's often basically what you need to group. And really, having a lowbie pull stuff off you is great. It's not like there isn't too much loot for everyone anyhow! The only problem comes in situations when you can't really help (like some of the poisonous zones or mobs).