Create extreme urgency.
On your sales page, after the headline, show a floating countdown timer with the price. The price is heavily discounted and goes up very quickly (5–15 minutes?) until reaching the full price. The timer shows how much time until the next higher price is set. This floating overlay follows the buyer as he scrolls and reads through your sales letter. The timer does not have to be the same for each step nor does the price increase, but the buyer can see what the next price will be. For instance, the first or last timers can be longer. You can also have a final timer after reaching the full price, where you give the buyer some extra time to buy it full price but also get a bonus. You might want to use this tool only on the second visit of the customer.
Help convert the ones who are just a step before buying.
When a visitor seems to be interested in an item (he spent more than average time on that page, scrolling back and forward reading, etc.), but then seemed to not buy the item and move on to something else (still on your website), you can pop up a one time offer that has a very short time limit (one minute should be more than enough.) It might say something like this: “Get XYZ for $79 instead of the usual $139 price. This offer is only good if you add it to your cart within the next 00:48 seconds.” (The time is an active countdown.) Once it’s in the cart, it should have a small text saying that the discount is only valid if they buy it during their current visit. This will help keep them from abandoning the cart and not finishing the purchase.