If you include soil tests as part of at least a few client's lawn fertilizing packages (and you should) then you already know what at least regionally is missing from their soil to grow this
useless and unsustainable crop. Manicured grass has a high N demand which compost teas will likely not provide to the extent that your clients are used to. They expect instant magical greening to make them happy, at least in the suburban world of North America. The typical kilogram of high nitrogen grass fertilizer might have to be replaced with literally much more than 500 gallons of compost teas in one of your brew tanks. I'm sure you've had it analyzed and realize that already since you have a business going on.
While I think that it's a great marketing idea (suburbanites will likely fall for the organic compost tea idea more than most - you seem know your market!), but in practice in the long run it may disappoint in results. You can pull the wool over their eyes in the beginning and make some coin, but eventually the stream of income will dwindle if the claims are not realized. So keep this in mind. IMO of course
Lawns are evil. I've never had one and never will. First thing I did when I moved to the suburbs from my farm was turned all the sod upside-down to decompose before planting far more interesting stuff. Yes I've even battled my municipality and local bylaw officers in court over it. And I won!