I mean if i send USDT and get BTC i pay 0,5 - 1% fees to fixedfloat + the fees for BTC network that i got the BTC.
If i send BTC to get USDT in ETH Network i pay the ETH Fees and the regular 0,5 - 1% fees but i pay more to fixedfloat, i pay also fees for BTC but why? i mean if i send i already pay fees for the sending of btc.
Because every on chain transaction requires a miner fee which as you may have guessed with the name, goes to the miners. Some exchanges though inflates their withdrawal fee, I'm just not sure with fixedfloat since it's an instant exchange and how much in percentage. In any case, most exchanges will ask you to pay for it.
If you're looking for instant exchanges, try exch.cx as they're pretty transparent with the network/miner fee.
I check Trustpilot for BitMart and MEXC it have really bad reviews in last time? how can i find out if i can trust a plattform? is here any topic for BitMart where i can read about it?
To be fair, all, if not most reputable custodial exchanges have poor reviews on trustpilot.
To name a few:
Bybit - 1.9 overall score
Binance - no overall score but 66% is made up of 1 stars
Coinbase - 1.5 overall score
Kraken - 2.0 overall score
Kucoin - no overall score but 76% is made up of 1 stars
For starters, ignore trustpilot, it's not as reliable as you think.
We recently had a discussion about mexc, check it out:
Opinions on Mexc GLobal