If the sole reason for this suggestion is to make credit-based auto shops feasible then I am not sure it is the best way of going about it. The suggestion seems to have a little too much emphasis on making it seem legit - paper money. The problem with that is credits are not in any way/shape/form legit. They never were and may never be part of vanilla minecraft (I understand Minerealm is not pure vanilla MC but if paper was chosen to make it seem legit then the fact while paper is legit, credits are not seems to be missed).
Credit-based autoshops, IMHO, would be best served in one of two fashions: By making it possible to pay a player and get a redstone pulse as a result (like a reverse command block but that would in no way be legit) or by some kind of back/deposit system. You would pay a "bank" (maybe the autoshop) with a command like "/credits give supershop 500". The obvious problem with this is how does the autoshop "know" how many credits you gave it and what item you want to buy. I understand with a paper system it is feasible to feed a hopper with paper "money". If you feed it the wrong amount it will spit it back. When given the correct paper amount (which it can determine via a sorter) it will dispense items when the correct paper money is deposited. The problem with that is even a single sale point would require exact paper cash, IE one 500 credit paper for a 500 credit item, requiring the payee to (probably) make currency on the spot, or a very complex redstone sorting system to support a single transaction. All so that we can use paper credits instead of items.
Going back to the second suggestion I made. While a single deposit "account" for an autoshop would simply not work, a deposit account for each sale point would fix one of the two problems I mentioned. However, you would still need to signal the dispenser to dispense the item for sale.
My counter suggestion/proposal (the paper money suggestion is a good one, just not what I would prefer) is this: For every item for sale at an auto shop you would place a sign with four bracketed lines in a specific format. The fourth line would be the players name who placed the sign. This would be an indication to the server that you are placing a "special" sign. The specific format of the other lines could be decided by whoever codes it (sorry intelli) but would include the name of the autoshop/sale point and the amount of the item for sale. A player would simply need to use the command "/credits give <shop name> <amount of item>". The mechanics of the transaction would be determined by whoever codes it (again, sorry intelli) but could debit the players credit total and then credit either an account set up by the server when the sign was made or credit the player that is to be payed directly. I don't know enough (anything really) about the minerealm credit system to know if players accounts can be credited while they are offline. It seems to me that if you are crediting credits to a piece of paper you can credit them to a sign. The same mechanic that does not allow you to give more credits than you have or buy a realm when you don't have enough credits can be used here. If you don't have enough credits or you try to give too few credits the command will be rejected. Conversely, it could be coded that the command was not for a specific amount but for a specific sales point. The command would check to see the price that was set when the sign was made and if the player has enough credits, debit it from the players account. The only non-legit part of that system is a redstone pulse would still need to be generated. The "non-legitness" of this would be mitigated, IMO, by the fact that "real" (non-spawned) items would be dispensed and such a signal could only be produced when a player makes a sign and creates a sale point (formatting the sign as required) and then another player gives credits to that sale point/sign.
I know this is not the kind of response you were looking for LARDIMUS_PRIME. I was a little taken back by the suggestion using paper. I suspect intelli was thinking about something along the lines of transactions between players online and offline. The new guild system may even have had provisions for this. I think my system would be about as easy/hard to code as paper credits. It may be easier to take taxes from paper credits (or not). A paper system may even be closer to what intelli was thinking of implementing (and you know he has to be thinking about it, he is about 10 steps ahead of us concerning development of minerealm).
I hope you do not take offense to my suggestion and feel free to take it apart at your discretion.
