1) "Why is it that rich people can hire good lawyers that do their best to make their client innocent"
Umm, you already answered that yourself: they're rich and have the means to hire a solid attorney.
2) "What are some problems with lawyers?"
This is the common thinking that most people have, just seeking to find something or someone easy to blame for problems. Have you ever thought that the SYSTEM functions the way it does, which allows for things that you see as being less than ethical? Lawyers don't bribe people, don't threaten to break people's legs, or anything like that...they find parts of the system to address their case and interpret them to the body listening (jury, judge, etc.) to show how their client is accused falsely.
And if that isn't possible in a specific case, then the lawyer bargains with the state to give them a certain ruling in exchange for a certain punishment for their client. In either one of these cases, the ability to do so exists within the system. So why are you, like everyone else, wanting to blame a lawyer for knowing the law?
Do you have any examples of actual injustices committed?