I love Greenthumb. These are the guys that spread magic fertiliser stuff on your lawn four times a year to make it look lush and green. Why is that so special? Why not just buy the magic fertiliser stuff from B&Q and do it yourself?
Because it costs more to buy it from B&Q (or any other DIY store), even before you account for your own time trying to spread the damn stuff over your lawn. And it takes ages and ages to painstakingly pour n grams per square meter over your whole lawn.
So, for £21 a time, a lovely chap from Greenthumb comes four times a year and treats our lawn. To buy enough fertiliser to cover our (quite small) lawn does cost more than £21. That is a great business. Imagine if you were a restuarant and you could provide your customers with a gourmet meal for less money than it cost them to go and buy the ingredients in the supermarket.
I don't quite understand the economics of Greenthumb, but I am guessing that:
(a) they are (obviously) paying a wholesale price for the fertiliser stuff
(b) they can spread it over a lawn in a tiny fraction of the time it would take the lawn owner, because they have bought (one) somewhat expensive fertiliser-spreading machine which it would be uneconomic for a single lawn owner to purchase. I've never actually seen Greenthumb administer a "treatment", but my wife tells me they are in and out in less than five minutes
(c) because they don't need supervised access, they can schedule their appointments to perfectly optimise (I like split infinitives; I think it is better to split than cumbersomely not to split one) their own travel time. So they do (I am guessing) a dozen lawns all within a stone's throw of each other, on a particular day, getting a good £250+ revenue per day. And presumably a lawn-treatment-dispensing person costs about £80 / day to employ (less?), minus (say) £5 a pop wholesale cost of the fertiliser, leaves you 40-odd% gross margin.
Then they charge extra for mechanical things over the winter (aerating and that sort of thing, which could easily add 50% to their annual revenue from each customer, if we are anything to go by), so all adds up to a good little business.
Plus they can charge extra to fix nasty things like leatherjackets (cranefly larvae, which live underground and eat grass roots, turning a lawn into a patchy brown area with some tufts of grass). Once you have a beautiful lawn, you are very, very ready to pay a bit more to keep it that way. (I speak as someone with a recently-cleared-up infestation of leatherjackets)
And, finally, I like them because they are focussed. They keep your lawn green, that's it. They don't mow it. They don't weed your flowerbeds, sell you compost or prune your roses. They don't do anything else in your garden at all. They just do lawn-fixing. There's a lot to be said for that - every additional thing you try and do inevitably reduces somewhat your expertise in your core area.