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 where is the top and where is the bottom. That is not something anyone can predict with 100% accuracy.
Otherwise every trader would be a billionaire.
I know it can't be predicted, but there are some lessons we learnt from the past that how could a coin react. Also, when you look at the chart, you can notice a coin pumps suddenly, even when Bitcoin and other altcoins are not increasing. If this is the case, then the coin suddenly increased won't sustain longer, and it would dump again.
Of course, there is a chance that it would raise more; that risk you have to take at least if you want to make profits. However, you aren't selling at a loss; possibly you may miss more profits in case the coin raises more. It doesn't matter either know the top or not, but from the sudden pump, we have to get an advantage by taking risks.