With all work that you buy there is an element of risk involved no matter if it is an established round or a newly canvassed one.
I would suggest that 95% of domestic work is based on a verbal contract and therefore you have no guarantee they will be loyal for any longer than your last clean.
So, from a purchasing perspective you have to look at how long it wil take before you have made a return on your investment. Look at if you have employed staff to do the work, the cost in doing the work etc..... then work out your period of time required before you make a return and then justify if it is a worthwhile investment.
As a general 3 x the value will take you 6/7 months before you make any money - that is a long time to work for a return as peoples circumstances change, lose job, move, don't like you, don't like method, not happy with standards etc.... these are variables you need to consider when purchasing.