A few weeks ago, you may recall that I made a completely unnecessary personal purchase of Fury of Angerforge, ostensively to twink out one of my almost-85 alts. Even after both the DK and Warrior hit 85, I held off, as increasingly it is becoming apparent that my love of certain classes revolves around individual abilities and not the total package. For example, the first time I saw a warrior Heroic Leaping from the AH to the bank, I knew I wanted to level mine up. As a paladin, I have mobility-envy all the time anyway, but the ability to just kind of get goofy on a minute cooldown? Sign me up. Hell, I would have race-changed to Worgen (or goblin even!) had that race been able to be paladins.
Anyway, as it turns out, you spend a lot of time rooted in PvP, as a warrior. And without a healbot, you die rather quickly. I probably spend an equivalent amount of time Feared on the paladin, but the uselessness I feel is greater rooted as a warrior than Feared as a paladin.
In between the purchase of the trinket for 28,500g and my figuring out whether the warrior was for me, I was listing the Angerforge trinket on the AH for 45,000g. I had zero expectation that the trinket would sell for this amount. The principal here is simple. Sequestered away in my bank, the value of the trinket is effectively zero - I wasn't planning on selling it, but I was not using it either, despite having spent ~7% of my liquid bank for the option; I consider the initial 28.5k to be sunk costs. Meanwhile, if there even existed a 0.1% chance it would sell for 45,000g (a return of 16,500g), that would be worth the periodic 10g deposit every few days. Worst case scenario? I equip it on one of my toons a month or two from now and am out ~150g over the course of the month, which is minuscule compared to the kind of gold I write off as business expenses, e.g. canceling and reposting cut gems.
Then, I got this surprise:
Using the AH as your bank is not always feasible, of course. For example, there is no real point in keeping stacks of 400g Hypnotic Dust in there. Okay, well there actually might be a point in doing that, but not in the sense I am talking about today. Epic BoE items work amazingly well for this principal, as the supply is understandbly limited. Some crafted epics work as well, like Tsunami Decks.
In any case, when choosing your price, the important thing is not chosing a price based on what you would consider a good return on the "initial investment." That term is in air quotes because (presumably) you did not buy the item for its investment properties, but rather for your own future use. Rather, choose a price at which you would feel good about losing the future utility of the item. This isn't about opportunity cost, this is about pricing items that you had not planned on selling at all. Angerforge at 28.5k was at the upper end of the bang-for-my-buck scale. Flipping it for 35,000g might have been a reasonable return for some people, but an anemic 19% return on five-digit investment is not good enough for me. Nearly double that percentage though? Now we're talking.
Let me use a more pedestrian example: Inferno Rubies. I have a bunch of cut gems up on the AH at any given time, but I always try to maintain at least 10 uncut Inferno Rubies in my bank. Why? Because the absolute last thing I want to happen is to get a new piece of PvP gear or whatever, not have any Inferno Rubies to socket into it, go to the AH, and suddenly see that Inferno Rubies happen to be at 150g or something ridiculous. The personal value of the 11th Infero Ruby in my bank is signifigantly less than the first 10 - I would sell the 11th for whatever the market price happens to be at the moment, but the other ten would have to be at least double that for me to sacrifice the feeling of safety that having them conveys.
So, what I suggest is for you to head to your bank, take a gander at all of the varied sort of sellable knick-nacks or epics or stockpiled goods, and simply put them up on the AH for a price you feel is high enough for you to have justified selling them at to begin with (instead of warhousing them for the indefinite future) and see what happens. Most, if not all, will come back to you and you'll be out the deposit cost. Sometimes though, you will be that one guy out there with an item that someone else just cannot wait until tomorrow to purchase at a fraction of the cost. Being out there is always better than not.
Either way, enjoy the extra bank space.