Direct Email is tricky and must be done with care. Just don't let that stop you from discovering the path of ethical email.
If you are a jerk and only in it for the money will will without fail run into trouble. A jerk will out. And eventually someone will complain to your ISP in such a manner that you end up being bumped. If you are an intentional spammer then yes there are tricks you can use to avoid these problems. But that doesn't make spamming appropriate -- just possible.
If you are not a spammer than don't behave like one. The next time you receive a piece of spam ask yourself what about this email brought me to the conclusion that it was spam? Then don't do that.
For us the answers are things such as:
Now that you have isolated the various clues which indicate spam. DON'T DO THEM. Good email habits are that easy. And an effective direct email program is that easy.