Very simple stuff. Create business, build business, accept btc and buy your own service with your own btc. Pay the small amount of tax and you have clean money. One simple method of hundreds or thousands out there.
Lol it looks like you've experienced to eliminate the traces after carrying out illegal activities. indeed with bitcoin you can do the laundering of money, so that you will avoid taxes or else
It is not that easy, someone that look at the blockchain will see all the transactions come from the very same address and will realize that either someone is buying your service over and over again or you are the one doing it.
See every time the person will not send through the same address he has the ability to change it different address in order to do multiple transaction, how can people will identify if he keep on changing multiple address means, these thing should be take care so that we can control money laundering through bitcoin.
It wouldn't be too hard to trace those bitcoins from the first address to the last with all in between, remember that all the transaction take place on an public ledger.
They can use mixers along the way and that would help a little but if you are talking big money then no mixer can handle it.
And what sort of "control" are you talking about, government laws and regulations? No way man, if they want to catch tax cheats then they will just have to find another way.