They are an excellent resource for raising money for capital improvements. However, for accuracy sake, they should be referred to as transfer tax since few apartments are flipped and the fee you want to charge is not a flip tax which refers to a buy and sell in a very short time created solely for the purpose of making a profit. A transfer tax is used when the traditional buy/seller transaction takes place. It is an easier way to reaise revenue than constantly raises maintanence fees. Buyers would need to understand that it is just a cost of getting into the building and preserving the amount of increases to the lowest level and owners, that it is an expense for the profit made on the unit as a result of the quality of the building. This must be done using an excellent attorney who deals predominently with co ops. Your average real estate attorney might not know how to do this and protect your community. The charge can be to either the buyer or the seller or both and should go into the capital reserve account or a similar one so that there is no question as to the purpose of putting this into play and where the money will be used. Good luck, this is a smart decision.