when and how the fee will be applied?
If fee is set to 1% and you deposit 100 mBTC then 1 mBTC will be auto-donated and you will receive chips worth 99 mBTC.
If fee is set to 1% and you deposit 99 mBTC then auto-donate would be under 1 mBTC - you will receive chips worth 99 mBTC.
Current fee is set to 2% so depositing 50 mBTC or over will result in auto-donate.
I also support the fees of 2% but how we differentiate between the normal client who wants to mix his coins and the other guy who only wants to exploit the current situation?
We cannot. It would require tracking our users.
I recommend that this be put somewhat clearly in the site, as people who have used ChipMixer before, and even those who have not, could not know about this fee and would complain about it afterwards, potentially hurting ChipMixer's already established reputation. The way it is right now is easy to miss and conflicts with the information in the FAQ. Updating the FAQ would definitely help in this case.
Information is set in bold above deposit address. People who used ChipMixer before would not read FAQ every time before use.
FAQ will be changed after permanent decision about fees will be set.