Bob, while your advice is good I think 600 Euros + a day sounds incredibly optimistic. Visualisation is becoming a fairly general skill in the marketplace. A senior salaried architect in the UK may earn the equivalent of 300 Euros a day if he is very good. Rates in other parts of europe may be less, so I would be surprised if a visualiser will achieve the rates anyway near the above. If he can earn 25+ Euro per hour as a freelancer I think he will be doing well. If he has a studio that carries costs he may be able to do better but a lot of practices will go for a cheaper alternative.
When starting out it may be an alternative to build things up on the basis of working out what your basic expenses will be, add on top a little bit for the drinking budget, traveling, annual holiday and a little profit of 15% , divided by your estimated working working hours in the year to get to an hourly rate.(- And dont forget the Taxman!) Then once you have built up a relationship with the client after a couple of months you can negotiate a little more. Once you have a foundation with a few initial clients, it will allow you to price more aggressively when approached by new clients - which is where he can make some money.