The quality of your customer base is one of the main factors influencing the multiple used, dave is spot on.
Think about it, where else can you buy a business that has repeat monthly turnover and profit where you start to break even on month 4, 5 or 6, most businesses will not even think of breaking even until year 2 and 3.
What a great return on investment.
But first check when it was last cleaned, contact every single customer, make sure the seller has contacted every customer of the new change, and even then you may still experience cancellations.
Regards
Nath