And it could be true! Some gardeners do hold the correct qualifications and insurance to charge you for using chemicals in your garden, but the majority do not. If that does not bother you, it is certainly none of our business, but we suggest that it is worthy of your consideration.
Even Gardeners who can legally do this type of work for you, will be unable to purchase the range or quality of raw materials and equipment that we use. They simply do not have the economy of scale, purchasing power or relationships with manufacturers that we have.
Quite frequently we are called upon to undertake work on lawns at properties where the gardens enjoy the most thorough attentions of highly qualified professional gardeners. Often this is because the gardeners themselves have recommended us, or called us in themselves.
You can get your general gardener to do lawn work for you, they might even do it without breaking any laws. But in most cases, it would not be a logical, economically sound or results driven choice.