The chances of picking an exact top (or bottom) in the market is unlikely in the extreme. It's also not necessary to make a profit.
Capturing the trend will provide substantial rewards. There's no need to try to squeeze out every penny, and traders who try usually hang on for too long.
There are the signs:
1. The first sign of a market top is a decline in the number of 52-week highs.
2. The second sign is a decline in the rate of advance of the NYSE. That shows overall weakness.
3. The third sign is a new lower low on a down day. The uptrend has failed.