I've been spray tanning for about 6 yrs, have used a couple of brands and now use Ecotan by Sudo. I have never had any problems and my clients all dress straight away.
I close my nozzle over so that the spray is a very controlled, fine mist which allows me to stand very close to the client, my gun is literally about 12 inches from their body.
The tan is therefore "dry" upon application.
It sounds like you are using too much tan or that you are standing too close with the nozzle too "open."
Close your nozzle fully so that nothing comes out when you pull the trigger and then tweak it slightly so that you can just see the mist. It works for me, no runs or wet patches and certainly no complaints.
Don't forget that as long as the tan has touched the skin then it will develop, you need a smooth and steady action following whichever tanning pattern that you use... Face and chest first etc.
Keep your gun moving to avoid product build up in one area, when this happens it tricks your eye into thinking that everywhere else is White so then you end up respraying and the client gets wetter and wetter.
I'm a bit rubbish at explaining things but I hope this helps xx
