Using adwords to promote affiliate products.

If you are using adwords to promote affiliate products how do you know it will be a success? What kind of research do you do?

I recently tried to research keyword traffic estimates on Google adwords only to find out that their system is down. I spoke with the helpful gentleman at Google. He suggested that I look at the global and local monthly searches to get an idea of what the traffic would be. This tool also will give you an estimate for cost per click.

Well the estimated cost per click when you look at keywords in the keyword tool must be for position 1. It was way too high. I want to know what the estimates would be of cost per click for positions 3-7. I'd also like to know what the estimated traffic would be for these specific positions.

For example, will positions 3-6 give me 300 visitors a day if I set my cost per click at 30 cents per click?

I know these are just estimates but I'd like to know an approximate idea. From an approximate guess I could tell how to go from there.

I could say nah! Forget this! Or I could say ahah! This is it! But even if I think I have a winner, the way I'll really know (assuming my ads and my landing page and my content all match up) is to see with a large amount of traffic.

A large amount of traffic tells you the trend. From there I could try different ads or something, etc.

Does anyone have another suggestion for getting around this dilemna?
I'd like to know before I get all sweaty and in to promoting an affiliate product how using adwords to promote affiliate products will turn out.

Since Google won't tell me perhaps someone else has another solution.

Thanks in advance.

Also, this is my first day as a part of the warrior forum. I think this is great! It's nice to have such a nice bunch of brilliant minds working together to help one another. Thank you all and I look forward to your replies, etc.