no, you can't get banned for having shit ratio
I have many accs with ratio 0 or 0.01 or other shit ratio under 1 and no problems since 2 years. And eventually if they warn you and pm you just pm em back telling them you got shit internet 1 mb download and 10 kb upload so they will leave you alone. Don't be stupid to stay and upload for them leaving your PC open and consuming electricity ->> more money at bill. Be smart, act wise.