Lots of stores have self-checkout lanes now. That’s clever. They get us to buy their goods—and do their work too. Instead of paying cashiers to check us out, it’s like they’ve enticed us to pay them for the privilege of a rewarding work experience at the end of our shopping excursion. Now, using this principle, how can I sell my love to someone, and be able to not only keep it, but get more in return from the very person who bought my love in the first place?