If I were sold in a top or near-top, then I could buy it again at a cheaper price. Also, I would have a handsome amount in profit. What do you think?
That what you are describing is literally trading. And yes, you can trade and make a profit but the reality of the problem is knowing what is the top and what is the bottom. That is not something anyone can predict with 100% accuracy.
Otherwise every trader would be a billionaire.