If Odin has no limits, he doesn't need the characters to do fetch quests.
Right, but who's saying Odin has no limits? Not me.
And who's talking about fetch quests? Again... not me.
Your idea was beautiful, I gave you XP for it but like
@Crimson Longinus said, Pandora's box is now open. (See below)
That is not the point. If it works for Odin, why can it not work for Freya or Thor or Lolth? This is how players think, this is how I think from a world-building perspective.
Do any other player characters have relationships with Freya, Thor, or Lolth? Is this bound to come up? Will whatever idea the player has line up with things relevant to those deities?
Odin is connected to secret knowledge... it's part of his lore. So is the idea that he sacrificed something to get special knowledge.
So, if a player had a character that had a relationship with Lolth, and then made some kind of plea to her for aid, and it was something that Lolth may have found interesting or worthwhile, or similar to something about her... yeah, I'd try and roll with it. Incorporate what the player is trying into the game instead of saying "no, that doesn't work".
Now, I will say that this requires some amount of discipline on the player's part. But I've not really had that problem since my group and I were in high school. Everyone I've played with for the last 20 years has been able to contribute to play without it being some attempt to cheat or avoid challenge.
And how would you limit it? How would you say no?
I'm curious to see how those with different playstyles would say no.
It has to be something constructive, not Odin doesn't require anything, I cannot think of something creative or only requests about knowledge of something secret work because all this is DM decides
Well, in
@Oofta's example, the player was demanding the outcome. So, I would say... "Odin's not just going to give you what you want. Do you really want to see if he can help?" and then if the player wanted to proceed, I'd have Odin (or one of his valkyrie or other servant if necessary, it doesn't really matter) present the offer of assistance with the caveat that it will come with a cost. As I said, I'd push the idea of this cost to the player to see what they had in mind. If they suggested something of minimal value, I'd have Odin (or his servant) scoff at them. "Odin gave an eye... the eye of a god... half the light of the world... what do you have that can measure against that?"
If the player still couldn't come up with something, then I'd try to come up with a suitable offer. Hard to say what would work from the example... the player didn't seem to care about anything in the game... but thinking of my players, I feel confident I could come up with something. It would vary from player to player and character to character.
If the player decided their character would not agree, then I would have Odin (or his servant) dismiss them and tell them not to waste their time again.
Nothing above amounts to the DM just saying "Yes, here's all of it". There is denial of what's being asked at several points.