Hi Wrighty,
I wouldn't give him more than 3 months turnover. This is the rate for quality residential work in most areas I know. After all, it is very easy to pick up res work in many areas. Adge, one of the members on forum has just started out. He went out canvassing for one evening (100 doors) Got about £90 of monthly work. If he sold that for 3 times that would be worth £270
. Not too bad for ONE evenings work
So, don't pay over the odds.
Commercial is a different story. 5 or 6 months turnover is more like it. This kind of work takes a lot more effort to accumulate in my experience.