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 like your closing statement, if everyone could accurately detect in 100% accuracy the tops and bottoms of every trading chart, all traders will be billionaires and there won't be any thing to leverage on. Trading is quite complicated considering that the market always capitalizes on fluctuations occurring as a result of the market volatility. If you're able to understudy the direction of the market fluctuations for the altcoin in which you invested or traded on this bull run, you will definitely make a lot of money and profits out of the system, but if it is otherwise, you might end up losing more than you predicted.