Aceepting Bitcoin is NOT tax fraud as bitcoin is NOT money, the EU courts have already stated this and there is no tax on bitcoin.
If he then spends the bitcoin he is absolutely fine, whichever way you want to try and look at it.
If he sells the bitcoins for cash/fiat via electronic transfer, he should really declare this as income which would be taxable once above his countries threshold, which is of course viewable by gov if done with electronic transfer.
As he can pay himself any amount of bitcoin he pleases in salary as it is NOT money,
it will have absolutely nothing to do with his businesses finances, as it is NOT money.
Accepting bitcoin is the same as accepting buttons for payment, and then paying yourself those buttons.
If he sells his BTC for cash there is also no record of any income, although i doubt this income would be taxable, unless a considerable amount.
in comparison, do you declare any income you receive when you sell your old items ?
i very much doubt it.
selling bitcoin for cash is just the same as selling old toys out the attic.