Could it be that it means that people don't think it's a good deal to sell at 500k and the price should be allowed to go higher?

I know very little about economics, so feel free to tell me I'm wrong and not waste too much time explaining why.

No - save for a war, which almost always causes deflation, the only thing that lowers the (real) cost of credits is cash inflation, since the dollar cost of credits are capped.  This simply continues the status quo and allows a small part of the economy (mainly CA's) to keep flowing in the prolonged absence of people selling credits.

Ah, completely ignore my previous statement.  I read your question completely wrong and thought you were asking why prices weren't lower.  Egg on my face.

I'm kind of on the fence about the idea of the market cap because it will almost inevitably guarantee it reaches a maximum price at some point, which makes it harder for those on the lower end of the spectrum to latch on - how many times have we heard complaints about the price?  As it stands, a CA guarantees a reliable return of investment that the market was slowly eroding with higher upfront costs.  Capping it prevented that trend from continuing, but with this prolonged absence of peace, it's also slowly starting to bog down the incentive to sell.  

Aside from taking in more users, the biggest thing in general that drives the sales of credits on the marketplace is exhausting the game's money supply, or making things more expensive - which doesn't do many favours for normal users.   Damaging one economy has a tendencyh to help the other, it seems.

Needless to say, it's definitely a tricky area.  :)

I don't think raising the cap would solve the current issue, as even when people were willing to pay over it for private sales nobody was looking/willing to sell. It's purely a case of people wishing to stockpile/people wanting to hold credits rather than cash/people not investing into new credits. If the cap had been 750k, it probably would have resulted in the same thing occurring, it's more to do with the current 'environment' of the game rather than the cap itself.

Have to disagree Satanta, people just value a credit at more than 500k. Remove the cap and people will sell their credits for a price that is deemed to be the correct value of a credit. And then supply and demand will sort out the correct price. Right now the price ceiling is just proving to be inefficient for sellers as they are losing out..not the buyers.

I'm aware of people offering over 700k/credit on IRC, when they were readily available to be bought on the market for 495900 or so. I'm not sure we can apply 'normal' open market principals to the game, as the realities of it are very different.

Some players don't/won't pay cash to play. Be it due to a personal belief or a lack of funds, it's simply the case. Others will. This discrepancy doesn't exist when discussing normal 'open market' practices, so skews the numbers.

If you die in the game, cash is lost while credits are not. This discrepancy greatly skews the numbers. 

The most important issue of them all... at some point, the benefit of paying RL cash gives far too high of an IG boost to the players willing/able to pay it. If/when that happens to a game, it kills the game. You end up at a point where nobody who won't "pay to win" plays anymore and therefore the ones who can/will pay have no need to pay as there is nothing for them to benefit from as the game is now dead.

There are a dozen more that can/could easily be thrown out there. With that in mind, what is a 'correct value of a credit'?

The current cap is there in order to keep balance and not let some players gain an unfair advantage due to RL circumstances. It becomes dangerous if the cap is entirely removed and there is no checks and balances on what can be gained/achieved with RL funds.