hi there
even if this isnt a scam it is frought with issues.
what exactly are you buying ?? in truth not a lot. most domestic clients arent tied into 12, 24 or even longer month term contracts, with full t and c's.
therefore as soon as you start the cleaning, what is to stop them terminating immediately.
at best these clients can be approached as warm leads, ie they need to be converted by you to your clients, and work your way and to your costings.
therefore what is the value ?? worst case scenario its a mailing list .
at best assurances from the clients that they will stay with you for say 3-6 months, then invoice less expenses = profit x a multiplier calculates the value of that client and therefore starts to create a purchase price.
are they selling the kit. the phone number, website etc, any existing advertsing, all of these items will add up to another value, plus GOODWILL.
so let us know where you get with this
regards
martin