I would firstly get some idea of the level of clean required.
Sparkle
deep clean
end of tenancy
mid tenancy
fussy old bat
OCD
Then the jobs to be done in each ie.
oven
carpets
windows
bathroom
kitchen degrease and so on
calculate the time you need to complete each ie one bed flat 2 people for 8 hours = 16 hours
set you rate of pay per hour or day rate for your employees
calculate how long it will take and add 20% for snagging
add petrol chemical, equipment hire and running costs
See how much you feel you want to earn out of each job.
If the job is too much for you or doesn't pay enough to cover costs and give you a profit worth having then just walk away.
Better to wait for a ripe apple on the tree than to eat a bruised windfall.