I like to do it based on the ad spend, not the total clicks, because clicks can be arbitrary. I personally like to spend the amount of the payout on clicks per keyword. So if your payout is $10, and you've spent $10 in clicks for a single keyword, then pause that keyword if it hasn't converted for you yet. If it's an offer that you absolutely know can work, you can up that to 2x the payout, but it depends on your budget and tolerance for pain.
Not saying it's the best, it's just what I've done.
Yep. The 2x rule is what I do for keyword level stuff as well.
As some of the other posters have already pointed out though, it's not as simple as giving a number of when it's time to shut down. There are a lot of variables at play. How much you're willing to spend in test is a big one. How many other untapped GOOD ideas you have to make it work better is certainly another. I think knowing "when to say when" comes with experience, and there isn't anything on WickedFire, or on any other forum, or in any e-book that is going to legitimately quantify that for you.
Me personally, I'm relentless when it comes to promoting a new offer. I think it comes from working on the merchant side for so long, where when something doesn't work you aren't afforded the luxury of swapping it out. There isn't a choice but to make it work. That can be a good thing and a bad thing.
My personal process is pretty simple. Pick an offer I think can be a winner, create LPs and initial campaign strategy. Get as much cheap traffic as possible to make good assumptions about what the performance is going to look like. CTR from the landing page to the offer if a LP is involved, CTR & split testing on the ads, offer conversion etc. Optimize, optimize, optimize and then get creative and then optimize some more. Swap out comparable offers if I feel like I have the other stuff as right as I can get it.
At that point, it's just a "gut" call. If I feel like I have a winner, I keep pushing, scaling and working on new ideas to increase volume and profitability. If I don't, I cut my losses and move on to the next thing.
Everyone is different, but I think it's a better approach to really exhaust all resources before moving on (within reason). If you don't get in the habit of trying to do that and are constantly offer swapping you are more than likely leaving money on the table. Also, as a side effect in my opinion...this process makes you a better marketer and makes you more intuitive about what's going to work vs. not.
My 2 Cents...