I didn't want to interfere with another Adwords thread where the OP was asking questions.
I've been running Adwords for seven years with less than stellar results. Looking back over the entire period, my cost per conversion has been $154. The items I've been advertising don't usually make that much in profit, so Adwords has been a net loser.
I have some of the best prices for products I advertise. I put the prices in the ads. I use model-specific keywords so I only get the people who know what they're looking to buy. For example, I have XY7GS Widget as one of the keywords, so I only get people who are looking to buy the XY7GS model. I don't want tire kickers. They were driving my Adword costs through the roof.
I have a very well-designed, well-functioning, easy to understand site.
I've talked to people at Google, but all they want to do is tell me how to get more clicks. I know how to get more clicks. I want more conversions.
Google Shopping was doing fairly well for me. It was doing better when it was free, as my products showed up all the time. Now, though, my products fall into one of the "prohibited items" categories, and I can't list there.
I don't know that there's a solution to my problem, but I thought I'd just rant and see if anyone had any advice. ;)