too quote someone else's description of what they are from another forum :
"These are the national contractors. The ones who handle the cleaning accounts for businesses throughout the country.
Why are they called MMM's? It's because they come in and operate just like the mafia. They control the market in an underhanded low balling way. They will push out the little guys - the mom and pop business owners. They don't really care about you the contractor. Extracting the maximum profit is their only objective. Most pay pathetically low prices. And many will drag out the payments. They will ask for the stars and pay you only a pittance for your labor. Worst of all, they will swallow up the cleaning market in your area. National contractors are not your friends. They're the equivalent of Guido, they're only here to break your legs."
Most books on succeeding in small business urge that you be a "niche" player. Don't try going up against the large, impersonal, entrenched businesses.
Example: don't open "Joe's Discount Furniture and Appliance Store" next door to a Walmart. There's always plenty of business out there that is of absolutely no interest to the MMMs: premium quality residential work; small-to-medium sized commercial work, such as: funeral homes, country clubs, condo associations, churches and social/fraternal organizations, etc.