Major misconceptions here.
What is this ? Just like Star said, you pay x dollars so you will have the ad in a certain position. We will exclude the motivation of the publisher (the site owner) because he already got his money, so he doesn't care anymore about the ad.
Sorry, but us small site owners care way more about the advertiser getting the most bang for his buck than big sites or AdSense/AdWords ever will. I've helped people get the proper ad placement, after seeing the ads purchased, where I know they'll get the most traffic/clicks/ROI simply because I know my site best. I've also recommended changes to ads, recommended some banner maker I know for people not doing a good job at rolling their own, and in a couple of extreme cases even wrote a couple of text ads for customers!
Think AdSense does that?
Not like we spend much time dealing with this because most adverts are what they should be, placed where they should, but we keep an eye out for issues that need some TLC because I wanted repeated sales, not just a one-time sale.
A little customer service pays well too because my longest non-stop advertiser in my recurring billing system has been there 7 years, most of them have been with me over 2 years. That's right, recurring income, some pay monthly, others buy in bulk for discounts and recur quarterly, bi-annually or annually. I can depend on them for a steady income like clockwork, pay the bills, plan ahead.
Plus, the direct advertising methods are only used in top websites, while AdSense it's approved and constantly used on hundreds of thousands of websites.
My site and my competitors aren't big sites, but every single one of them offers direct ads. However, my competitors and I dominate our niche in top 10 SERPs which is why advertisers like us opposed to being placed randomly on any old AdSense site.
Some offer just banner ad buys, sponsored links or paid listings, others (like myself) offer a more complete solution with multiple ad location placement, specific pages, run of site, whatever you want.
do you use a custom solution to automate direct advertising sales or do you use a bought/licensed solution (if so which one?).
I am looking for quite some time now for something to automate this process.
Completely custom solution plus OpenX
To get started you really don't need complete automation to test the concept or start making money, just a shopping cart to sell ads, PayPal will work. The customers email you the ad content, you post the ads when they show up in your inbox ;)
The real goal, IMO, is to push recurring ads, as those add up over time as you gain more and more advertisers.
Advertisers don't always know if you're running other company ads or affiliates so pre-populating an ad system with affiliates will start the ball rolling. Some advertisers have even offered to pay to "replace" a competitors affiliate. Besides, affiliates makes a good ad system fill for remnant inventory.