[theturtletalks]

He did the filing with the tax form that company sent. I think the exchange he transferred from was sketchy or not confirmed. In that case, when you sell, they show the full price.

[astura]

I mean even if the exchange messed up and took out more tax than they should have, he would just fix that at tax filing time and get a refund.

If the exchange was overseas/super sketchy it's possible that the exchange just plain stole some of his money and claimed it was "for taxes."