In my opinion, the best place to farm gems quickly is act 1 inferno. In act 1 inferno, flawless squared gems are dropped, and those are the highest gems that can be dropped.
If you'd go to act 4 inferno, the same quality of gems would drop, but the pace at which you could kill enemies would very likely be much slower. Stay in act 1 because monsters are relatively easy there.
Obviously, keep your eyes open for resplendent chests and treasure goblins, but that goes without saying.
Determining the "fair market value" of an item is a chore at this point, although I'm certain that at some point in the near future auction house analysis tools will be created by Blizzard or the community.
Market value is likely to fluctuate considerably as people play the game in different patterns, so saying "X is a good rule of thumb," especially in the early going, is a losing proposition. Right now, for instance, low level crafting components are probably vastly undervalued as many people are playing low level areas. When the game starts to age, we'll likely see far fewer low level items, and more bits of high-level components.
Essentially the three pieces of information you're seeing are:
- The current lowest price available for you to buy the quantity of the item in question.
- The average sales price of the last 10 of those commodity sold, which is supposed to indicate the short-term trading value of the item. However, this is unclear as to whether the price is inclusive of "bulk orders" or not - if someone buys 100, what 10 of these count?
- The average sales price of the last 24 hours worth of sales, which is supposed to indicate the long-term trading value of the item. However, this appears buggy - at times, this has read 0 for extended periods, even though it's clear there are many sales going on.
If you're listing a commodity below the lowest price on offer, and then not seeing the buyout price change, that's because you can't buy your own auction - so you're seeing the next cheapest item for sale from another vendor. This is what you'd want if you're going for a quick sale, but might not be what you want if you're trying to maximize profit.
As far as pricing your own commodity auctions, I've found that only empirical data sampled over time is available at this time. For instance, I'm often buying Square Rubies, and I know that around ~8k gold is an "average" price - I see them listed for far less and occasionally try to buy, but frequently am out-sniped. If all I see is 10k+ gems on offer, I'll probably wait for a price break.
Selling is similar to buying, just in reverse. If you've got something you think is particularly valuable, sample the current values of the 3 pieces of information you have available, and then watch for times when the current market price is above what you've determined is fair. Then you can list your item slightly below this and turn a profit, or list it at what's typically "average" for a quick sale.
Best Answer
As of patch 1.0.4 the maximum gold find is now capped at 300%. The only exception is Nephalem Valor which can bring the total Gold Find to 375%.
Pre patch information:
According to datamining sites (example) the relevant item affixes are:
So, here is a try at the most possible gold find.
Total: 491%
There may be some legendaries with increased gold find, so more than this may be possible. However this is not at all realistic, because 1) it would take ages to find perfect "Prosperous" items for all these slots, and 2) your gear would likely be decidedly suboptimal for your class if all you sought was Prosperous items.
Overall, to maximize profit, I think you would do better optimizing for your class's DPS stats, and adding in as much gold find and magic find as you can without hurting your kill rate or survivability.