Good points, everyone, thanks for sharing.
One thing I look for consistently is a payout of 15 percent or higher. Once in a while I'll go with one a little lower if I think it's a worthwhile product, or one that will truly benefit people in some way and is from a quality, reputable company, but those are few and far between.
I started this rule of thumb about three years ago and it helps me weed out a lot of programs that never wound up paying anything anyway.
I actually tried running on program once that only paid 2-percent commissions! But I thought it might be something my visitors would like. I wound up sending heaps of traffic and not getting one red cent. Did not make me happy...

...wasn't worth the work or the grief.
Another thing I do is after 1000 clicks to a merchant, if there isn't one sale/action, they're out.

I'm not wasting all my work to advertise and help brand for free.
You find after a while that you have to set standards and be tough and stick to them. I pour too much of myself and my time into this to be playing any games and sometimes I can't help but wonder if some affiliates are honest.
I had one that owed me over $700.00 and just totally ignored my requests and finally the site was shut down. That was pretty rotten, IMHO.