A real trick.
Here's a trick that I saw used at a school in Ft Pierce , Florida back in the late 90's.
You pay for a 3 week PPL package. You are led to believe that if you need any extra training it will be charged at the basic rate - fair enough. Only when you reach 45 hours is the actual pricing explained. Your package price was based on the normal hourly rates and you had been given a discount for completing your course on time, result: package price. However as you hadn't completed your training on time you now foreit the discount and so your account was reworked with the flying you had already done rebilled at the normal rates.
That school which I will not name, after a re-routing through various other Florida airports no longer exists. The owners however are still involved in flight training on the east coast of Florida.