Catching a blow-off top can be defined using a simple mathematical function, the chances of catching an accurate top are directly proportional to the loss you are ready to take for it. For example, the simplest method is the trailing stop loss method where you set a trailing SL like say 2% below the current price and your position will be sold whenever market falls more than 2% from any high, this way you can fetch almost high with lesser risk, the most risky method is to wait for a bearish divergence in higher highs, no matter how many divergences you see, there still are good chances that price can break another high, but this way you can sell at extreme top without any loss