But now after the fee has increased, it has been impossible to get profit. There's a transaction cost which I can not avoid and it is very high. I trade small amount like $50 even (To make a strong hub). In such cases, I have no profit almost unless I'm dealing $300 or over. That's a pain to pay such fee but I have no way because I do not make a bad relation with buyers and sellers.
This situation is also the same, this is also one of the problems that can actually be solved by the lightning network, but then a lot of people will do the same thing as you are trying to do so, less margin per trade for you.