Learn to say "no". It's freaking easy.

I do have a smartphone, and every time someone asks me to install something on it, or ask for my phone number for "accumulating bonuses", I say simple and dry "no" looking into their eyes. When there's a queue behind me, they'll just show loading icon on their face a couple of seconds, and then proceed, because of pressure.

Otherwise, when there are no more people, they feel like wasting their and my time, I just stare harder in their eyes, and they feel ill at ease and back up rather quickly.