We recently got a customers system connected who had brought through another provider, and left unconnected for 11 months . Due to the size of his system he has lost around $3700 worth of production during this time. Not good.
Unfortunately, this is not uncommon, and the reason for this particular system was, he needed and isolation link, a $100 product that the company wanted $2000 for.
Unfortunately again, if a company does not inspect your site they are totally within their rights to charge you for extras, and as there isn't any regulations on price for these types of things, however much they want as well!
Even worse for this guy, the terms and conditions allowed them to do this, even though they had seen the site!
Always make sure your quote is grid connected, as it's a nightmare to sort out afterwards if it is not.