What is a click actually worth?
Every placement decision comes down to one question people rarely answer properly: what is a visitor worth to you? Not what you would like to pay. What one actually earns.
Start from the far end
Take your last hundred signups and count how many became paying customers. Multiply that rate by what a customer is worth over their life with you. Now divide by how many visitors it took to get those hundred signups. That number is your ceiling, the most a visit can cost before the placement loses money.
Most people discover the number is smaller than they assumed, and that is useful. It turns "is this expensive?" into arithmetic.
Then look at what is published
On a board where click counts are public, you can do this before you spend anything. Take the price of the position you want, take the clicks the listing there has collected, and divide. That is roughly what you would be paying per visit if the spot performs the way it has been performing.
Two caveats. A brand-new listing has no history, so there is nothing to divide by. And the position can be taken from you at any moment, which shortens the window you are buying.
Not every click is the same click
A visitor who read a one-line description and chose to click has qualified themselves. A visitor who saw a banner has not. The same cost per visit means different things depending on how much the person knew before they arrived, which is the argument for placements that carry a real description rather than a logo.
The test after the fact
Tag the link, watch your own analytics, and compare what arrived against the public count. If the two roughly agree and the visits behave like your good traffic, the placement earned its money. If not, you learned that cheaply.