We have decided not to get involved at all with foreigners,after a couple of weeks cooling off period i have had less hassle of having to consider someone elses work.If jobs are being carried out on the side it is easier if i know nothing about it or have any connection at all.Whatever wages tech's earn it will always be nice to earn a little more!! and if these jobs are getting more regular it is bound to have some impact on the day to day running of the business.As Andy rightly says owners have put a lot of hard work and their own money and taken considerable risks in setting up their businesses.
This probably seems a bit mean but I cant remember anyone giving me a easy time when i started out.Apart from that,in a way it is the thin end of the wedge for your tech/employee to set up their own customer base and gradually undermine your own.

cheers

Colin