It's an all cash business.
Coin-op customers let the coin box of the washer or dryer act as a cash register and the owner gets paid in advance for the service. There are no account receivables and no delinquent accounts to collect.

It's recession proof.
Although it depends on the demographics of an area, a safe generality is that in good economic times, the wash/dry/fold aspects of your business gain momentum while in tough times, the self-service aspect of your coin-op laundry may represent a more major portion of revenues. Either way, the properly managed and promoted laundry will have hedged the bet against economic swings.

The market is constantly expanding.
With more and more single parent families and two-wage earner families there is an increasing market potential of people that do not have the time for mundane laundry chores. Aggressive owners have developed very profitable wash/dry/fold businesses doing customer's laundry for them.

There is no outside selling required.
With proper marketing, the customers come to you. Once they have tried your service and superior equipment, they become very loyal and quick to tell their friends about you. The only outside selling would be if you chose to develop commercial accounts, valet service, and the like.

Good equipment is designed to last for many years.
Unlike traditional laundry equipment that is virtually valueless at the end of a 3 or 5 year loan maturity, Frigidaire, Wascomat, Whirlpool and Huebsch equipment have many more years of profit generating capability and banks are therefore willing to provide long term loan amortizations.