You can lose profit sending trading and withdrawing if you are trading a small amount I have $50 worth of Ferum or FRM it will take $6 to send the whole amount to Bilaxy and after you trade it to Eth and wants to withdraw it you will have to spend $12 to withdraw your Eth,
now that's $18 gas fees for your $50, my only option is to trade it to other altcoins like DGB or Litecoin which offer $4 to $5 fee you still going to lose $11, that's over 20%.
That is the fact that we must accept, or jits better to hold for a while on your wallet. I have altcoins on my wallet that worth $10 or $15, but I let them sleep on my wallet because I know this is worth nothing and we have terrible fees of ETH as a gas when we are making transactions.
If you really need it to sell, try to calculate your net profit if you are going to sell your altcoin, less minus the overall fees. So that you will know how much will be left on you. Just like what happened to me last month, I sell a token worth $240 but my net profit was $200 something, it almost a $40 deduction including the withdrawal fee from the exchange. At this point, trade your altcoins to the coin that has a lower fee on withdrawal. Just like XRP.