I'm pretty agnostic about the 2c rule QuantumCat, and I did mention it in this thread already, 3 posts above yours. I understand the reason for the rule being introduced, and Andrew has given us some further detail below (or directly above where this post of mine will land in this thread).
Andrew, we have mentioned the volume matching, the 2c rule, that you have to have the available cash for a buy trade to go through, that the company must NOT be suspended from trading or in a trading halt, the 4pm cut-off time for orders, the importance of setting realistic limit prices, and that trades won't go through if the closing price lands on the wrong side of your limit price, however I don't think anybody in this thread has yet mentioned...
- The 20% rule. You will not be able to place a buy order where that buy order would result in that stock representing more than 20% of your entire investable balance (i.e. meaning more than 20% of your Strawman.com virtual portfolio total value). I recently explained this one too - and why it was introduced for Industry Super Funds for their Member Direct or Self Managed options - where people are basically using these industry super funds to create their own SMSFs.
TFG - you are correct, you will never know the closing price when you place an order, that is why I have explained that people should use a price that is as high as they are prepared to pay for their buys and as low as they are prepared to accept for their sells, because that will give you the best chance of your orders going through. You're going to get the closing price anyway, unless you stuff it up by using a limit price that is too high for sells or too low for buys.
TFG (Giant with Two Feet) - you are also correct about the buys and sells - the system will attempt to process ALL of your sells first, and then all of your buys. Because the system increases your "available cash to buy shares" every time you PLACE a sell order, you run the risk of some of your buy orders not being processed if some of your sell orders don't go through. I have explained before that you could hold 400 ANZ (I know you do TFG, in your Strawman.com portfolio) and place a sell order for 200 of those at $300 each. Your available cash to buy shares would instantly increase by $60,000, but that's an illusion because that sell trade will never go through because ANZ is trading at below $30/share so will not be closing at $300/share any day this week, month or year. Any buy trades you place with that "available" $60K won't go through because the ANZ sell trade won't go through. I think I used CSL as an example last time, but CSL actually would go through if you used a limit price of $300 for a sell, so ANZ is a better example on this occasion because ANZ definitely will not go through at that limit price.
So - to be clear - you can PLACE buy trades based on theoretically available virtual cash (meaning theoretically if ALL of your sell trades were to go through at the limit prices that you have nominated). However, when it comes time for the system to actually process those trades (/orders) they will only go through if there is actual cash in your account (still virtual cash, but not purely theoretical virtual cash). That's why the system does all of the sells first, to establish what your real cash balance is, before attempting to process your buys.
It might be a good idea to add another blog topic Andrew, perhaps called "Strawman Trading Rules" (or something like that) which list all of this stuff in one easy to find place.