How long does it take to clean?
MikeyL's figures work out at about £20 per job and he says they are mainly house fronts.
Now I know that St. Andrews can have some big Edwardian Villa houses, but £20 per front seems a very good rate. Bedminster ditto.
On the face of it it does seem a tad adventurous but if I was looking to buy then I wouldn't dismiss it out of hand - but it would certainly have to stack up as in:-
As described. (high on money, low on time)
Intro to all the customers and pay only those who agree to the switch.
Hold back some money (say 50%) until (say) the custies had three cleans and paid for them.