How credit-based ad exchanges work (and how to spot an unfair one)

A credit-based ad exchange is a simple deal: show someone else's product, earn credits, spend them to get your own product shown. The idea is old. Windows Phone apps traded impressions this way over a decade ago, and banner exchanges did it for websites before that. The details are what make one fair or not.

How the ledger works

1. You embed the network's widget. Each time it shows another member's product to a real visitor, you earn credits.
2. Each time your product is shown in someone else's widget, you spend credits.
3. The network keeps a ledger of both, so nobody gets more than they give, minus whatever fee the network takes.

Five things to check before you join

1. The exchange ratio and the fee

Every exchange keeps something back. Some keep a share of impressions and sell it to advertisers; some take a percentage of each credit. Either is fair if it's written down. If you can't find the number, ask for it before you install anything.

2. Whether views and clicks are priced differently

A view and a visitor aren't worth the same. Exchanges that price them the same reward members who show a lot of cards and send nobody anywhere. Look for a network that pays more for a click than a view.

3. What counts as a real impression

Bots, link previews, uptime monitors and prefetches can all load a widget. If they earn credits, someone is paying for nothing. A good exchange filters them and counts a visitor once a day, not once a page load.

4. How matching works

Who decides which products appear in your widget? Look for category limits, a block list, and a published rule. Watch for "engagement optimisation" with no explanation: that usually means whatever gets clicks, not whatever suits your users.

5. Caps

Daily limits on how much an account can earn or spend stop one bad actor from draining the pool with fake traffic, and stop one big spender from crowding everyone else out.

How Swapply answers those five

For transparency, since we run one:

• Fee: 10% of every credit that moves. Nothing is sold to outside advertisers.
• Pricing: a view costs 1 credit and a click 10. The host earns 0.9 and 9.
• Real impressions: bots, previews, monitors and headless browsers never move credits; one view per visitor per host per day.
• Matching: only your categories, a mutual block list, picked at random weighted by the square root of each account's balance.
• Caps: 1,000 credits earned and 1,000 spent per account per day.

For how the networks compare on these points, see our comparison of cross-promotion networks.