How do you guys deal with bads?

I'm not a mean person, but I invite friends and get invited by some that aren't so good..how do I effectively tell them they're not so bueno, and losing 600 points in my MMR is annoying. I'm not great, but it's hard to carry a game when people are almost ALWAYS out of position, don't ward, don't even buy a courier (I was mid Viper..spent good in the first 5 min on courier and upgraded it), yet they don't like to listen to suggestions, but derp around.
So solution A: no more ranked matchmaking with them, but queuing I ranked just means my win/loss suffers (below 50%...was almost at 51% in near 900 games).
Is it a better idea to suffer through training modes and make a smurf account? Just wondering, a kinda wwjd question, except for better dota players than I. Was around 3500MMR after test matches:.sitting 3 points below 3000, from trash tier to derp tier..

All of my friends in dota 2 are people who understand the game well enough and can play pretty well. I do not add anyone who is not so unless he/she is one of my IRL friends.

If I have a friend that is not good, I remove him/her from my friends list. Don't flame them in game, just remember to not put them on your side again as much as possible.

So... befriend only those that you know are good.

Smurf accounts are nice, but getting to level 13 is a real pain.