Some people are jealous or misinformed or whatever.

You can report yourself to a GM.
Basically say that you're boxing, and there is zero unattended play, you're in control of everything that occurs, etc.
Some GMs have said they can put a note on your character, and others have said that functionality doesn't exist.

As long as you're not botting, you'll be fine no matter how many losers claim to be reporting you.
Occasionally, in some games a lower/newer GM takes action against an account, but that is rare; and is also resolved once you escalate to a higher/more-senior GM who knows that boxing is fine within most games.

You can get addons so people below a level threshold cannot whisper you.
That is particularly good, if you kill opponents in PvP (world, battleground, arena, whatever).
People decide to compliment your abilities, by making a toon of your faction on your server to curse at you.
Either ignore them or remain polite (or get the addon, that forces them to be above whatever level (set it to 5th or whatever) before they can curse at you), don't be rude as they can report you for that.

You can make a hotkey:
/r I'm boxing, and in control of every action. There is no bot action. For more information, check out www.dual-boxing.com and www.isboxer.com

Make whatever hotkey you want.
If you decide to reply, you can tap that once to anyone who whispers you.
You can also ignore them.

I've found I had a lot of curious people.
And some haters.
In general the positive/curious outnumbered the negative/rude by a fair margin.