You can buy and sell and make profit.
You are right if we talk about the quality only.
It's true that you can double or even triple your money. But let's not forget the "quantity" and "time" here.
Quantity is how much money is required to be able to trade.
Time is how long does it take to be able to finally double it.
This also depends on the amount, if you just put the lowest amount possible, then you can just make a double in the slowest time possible.
it only depends on who is doing it!
if you are an expert trader or at least have some knowledge of trading you can make $1 into $100 in a short time and then work your way up the chain from then on.
and trading altcoins these days provides a very good opportunity for making huge amounts of profit even in a short time because there are a lot of movement in different altcoins with massive liquidity.