Rule 10. You must use only the stake money, and not 'stolen' or 'hidden' resources. You can use resources that you own and are fully paid for (e.g. a PC, Fax Machine, car, etc.) but these should retain their value after you have finished the step (e.g. you can't sell them to raise money!).
You should also avoid using anything which is part of an existing business run by you because the hidden costs are being born by that business and not by the system. Ditto for using your car, if the running costs are not being paid out of the stake money. Use common sense. The odd phone call 'on the house' or trip in the car is okay.
Running a taxi service using a car you already own, or making 10,000 copies of a manual on the office photocopier free of charge, amounts to stealing from outside the system. The doubling system should ideally 'stand alone', well apart from your normal employment and method of making money.
Rule 10. Detail. For example, it is not permissible to buy £40 worth of paper and then use the office color photocopier to run off fine art prints which you can sell for £80. Why? Because you are inputting more than the stake money. You are not counting the cost of purchasing and servicing the copier, or creating the original artwork.
In effect you would be stealing these values from someone else. The correct way of doing this would be to create the artwork yourself (or genuinely be given it, free) and then to go to a copy shop and pay the true price of color photocopying. I hope you see the difference. This rule says little more than "don't cheat".