I doubt you'll be able to make money from selling rare Pokemons. All the bots to automate Pokemon GO are already written and anyone can get hold of them. People are already botting the hell out of it and account prices went from 1000$ for a level 20 account to less than 5$ for a level 20 account in just a week. Once you'll be able to trade Pokemon, there will be already so many rare Pokemon that they won't be worth anything.
On top of that, people are already offering "Dragonite Services" for 10 to 20$ where they need half a day to bot as many Dratinis as they need to evolve to Dragonite.
I would say the Pokemon GO trade marked is already saturated with young people that are happy to cash in a few bucks after a day of work.