The merchant can offer free or very cheap delivery, while the customer participating gets large discounts.
Offer customers to help you deliver other packages in their neighborhood for a significant discount. If they participate, they come and pick up their order, plus all the orders in their neighborhood, and deliver them for you.
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.
Discounts and incentives cost you both money and branding equity. You should only use them when it seems the visitor will not buy. You probably already use simple timed or exit intent triggers to do that, but these are crude behavioral indicators. Something smarter is needed.
First, observe enough visitors to your site and see the behavioral patterns of those who buy and those who don’t. Time their visit, but also “follow” them around. Where do they go with their mouse on the page? What do they click? Where do they hover for longer time periods, etc? All this can and is already done today, but we need to take this further – use the information to match future visitors behavior. If there are distinct patterns that can predict a purchase, you can then only show the incentives when visitors do not match these patterns. Even better, if a “non buyer” pattern also emerges, only show the incentives to visitors exhibiting such a pattern.