You are asking the wrong question!
What you need to ask yourself is, what products can i promote and make good money with low refunds and that's it! If refund is low then its a 'serious' product.
You honored your title! You found the clickbank missing link!! Thanks man!
Well actually some people make good money with high refund products too.
If you make $5k sales a month and lose $1.5 to refunds, thats still a nice $3.5k a month profit irrespective of if its a 'serious' product.