There is actually no simple answer to this.
Firstly, if you are asking me if the blurb on the spray tan companies leaflets about 8 tans a day, meaning you can earn nearly 50 grand a year is true....then sorry the answer is no. Those sums neatly forget the vital little things like....finding 8 clients a day is hard work, and takes a long time to build up to. You have to buy solution and sundries...all of which cost money, fuel costs if mobile, or rent if not. They also usually work out their sums on charging every client £25 and never having to drop that price...the reality being that very few people can afford £25 on a regular basis, and its promotions that keep clientele regular....and regular clients are the ones that keep a business afloat!
However, yes spray tanning can be a good profitable line within reason. I would suggest not relying on it as an only source of income for the early days, do the sums yourself rather than believe what everyone else tells you and remermber that as far as the suppliers are concerned, they are doing it to earn money for themselves and what you see is essentially a sales pitch to get you to choose them over the next guy.
I have a reasonably succesful nails and spray tan business, although spray tanning is earning me the lions share at the moment, but I have purposefully not 'gone' 100% with any supplier, so I can always ensure I have the right mix of costs, quality and variation for my clients. I don't believe any one solution suits all...I use 2 or 3, and I identified the machine I wanted to use, based on my longer term requirements, before then deciding who was best (and not just best cost) to purchase it from.
I do however know of techs who have purchased a quick cheap machine that burns out after a few tans (the Argos one is a joke - the only way to true success in this industry is professionalism, so use professional suppliers), they throw together a home-made cubicle Blue Peter style, buy the cheapest solutions they can find, and then moan about tough times when their clients start coming to me for a professional tan applied in lovely clean, professional and relaxing surroundings, designed with a bit of thought for the clients privacy and comfort, and go home knowing their tan is perfect and gorgeous!
Food for thought, hopefully?