Does the fee work in exchange? No, you can setup fees only on the wallet (BTC, ETH, ERC send).

Example:
1. Bitcoin 1%, no less than 0.005.
1.1 if the user sends 1 BTC he pays 1 BTC + 0.01 BTC (your commission 1%) + mining fee (floating, check current mining fee here https://bitcoinfees.earn.com/ ).
1.2 if the user send 0.01 BTC, he pays 0.01 BTC + 0.005 BTC (“no less than 0.005”) + mining fee
1.3 if the user send 0.001 BTC, he pays 0.001 BTC + 0.005 BTC + mining fee

Please note. Sometimes mining fee is very high ($10+), we can not change it

For ETH and ERC calculation the same.

Q: Do you guys take a commission fee, other than the mining fees for sending BTC?
A: No, the user pays to miners and to you