Some tokens take a transfer fee (e.g. STA, PAXG), some do not currently charge a fee but may do so in the future (e.g. USDT, USDC).
function transferFrom(address src, address dst, uint wad) override public returns (bool) {
require(balanceOf[src] >= wad, "insufficient-balance");
if (src != msg.sender && allowance[src][msg.sender] != type(uint).max) {
require(allowance[src][msg.sender] >= wad, "insufficient-allowance");
allowance[src][msg.sender] = sub(allowance[src][msg.sender], wad);
}
balanceOf[src] = sub(balanceOf[src], wad);
balanceOf[dst] = add(balanceOf[dst], sub(wad, fee));
balanceOf[address(0)] = add(balanceOf[address(0)], fee);
emit Transfer(src, dst, sub(wad, fee));
emit Transfer(src, address(0), fee);
return true;
}
If you want to use the amount of token, you should use the afterTransfer amount because it is taxed.