How it works
You accept “tips” from your visitors and in return show some link love with text links or banners. Your visitors can enter a description for their links and these showup as tooltips when mousehovered over the link. Publishers can set a price for the tips and earn money from your visitors through scratchback system. Scratchback will take a cut from the payment you receive. I purchased a link at Scratchback to see how it works, see the image in this post.
To participate in this you need to register with scratchback for free and then place the widget on your blog. Visitors can buy links on your blog or site using the link in the widget.
Scratchback is in the early stages and i am not sure how bloggers will receive it. These type of widget links will have low CTR (see Blogrush results), visitors may not buy links at the first place to get traffic. But if you set a low price you may have some success with this. If you accept donations in your blog using buy me a beer or coffee link then you might try this one.