Her secret is three shades that are mixed to suit individual skin tones, combined with a precise air brush that delivers a fine, fast-drying mist.
"People can have their tan applied, get dressed and go to work without looking like an oompa loompa. It slowly develops throughout the day and doesn't have an awful smell or come off on their clothes," Susan says.
To get the best colour, make a booking two days before an event - a good operator will ask about colour, occasion and take into account skin type or time of year.
"A lot of people use a booth because they are embarrassed, but a spray tanner should make people feel comfortable and deliver the best result, not just a generic shade."
Susan uses Sol HQ, which is moisturising and sensitive enough for delicate skin types including those with conditions such as eczema or dermatitis - though anyone with pre-existing allergies should be spot tested first.
It fades like a natural tan and can last for five to seven days.
A full body application will set you back $50 if you visit her at home in Ahuriri or it's $60 for a mobile service.
At Urban Retreat in Havelock North, they exfoliate and rub on tan instead of using a spray.
Skin is assessed and exfoliated, concentrating on any dry areas and a few dabs of moisturiser are applied to knees, ankles, toes and elbows, which have a tendency to soak up more product.
"We use mousse and creams, and recommend a build-up tan so people can keep up the results at home," Corinne says.
"[St Tropez products] have a green base, which counteracts orange and it's got an aloe base so it's hydrating. It's also got a nice fragrance - the active ingredient DHA creates a reaction with skin that gives off a scent - but it's not a strong one."
A half-body exfoliation and tan is $70 or $120 for a full body glow.