Selling bitcoin for cash is a simple form of trading, but the complication felt is that it requires a banking link for each and every trade. Maybe this will cause a taxation issue for the trader. In some countries the taxation too is made upon the transaction we make with relation to the bitcoin buying and selling.
For the bitcoin atm machines, I never heard of a taxation process so far. Maybe it's tax free or the machine charges the tax with its usage fee, I've never used it before. If he deals with a local buyer, he wouldn't pay tax actually, it's only $2k as he tells.