As Pete pointed out. Pass on your tapes for others to learn. You no longer have the tapes and are sharing. And you've passed on something that has the consistent quality that was originally provided by the company.
Sell copies and you are robbing the buyer of the entitlements of throughly benefiting. They do not receive the personal coaching. There is usually important additional material that is not provided. Robbing the recipient of important data that helps make the best use. The quality of the copies are often such that important points can be missed or out of sequence wrongly named that causes more confusion than benefit. Factors that make it much more difficult if not impossible for the recipient to truely benefit.
If you really want something or really want to do something it sometimes needs to be difficult to obtain for the individual to truely appreciate the wealth of their goal.
Alex