Depends on the niche. I do not sell shoes but I understand that in that niche reversals are always in the 30-40% range. In my primary areas of home and garden products, the normal rate is under 10% (most merchants less than 5%) and I would question keeping any merchant that exceeds that for more than a brief period.
More important is why are sales being reversed. No reason or meaningless terminology is bad, bad credit card is acceptable, a specific problem with a specific product is ok, but repeated reversals because products are out of stock or otherwise unavailable are totally unacceptable.
I very rarely have had reversals due to tracking issues, such as "wrong referral" or similar, but if I saw that happening, I would inquire and if no satisfactory response was received, I would likely drop the merchant.
Since June 10, 2012 a vegan aarf but still writing the Hound Dawg Sports Blog
"If you don't have time to do it right, when will you have time to do it over?" -John Wooden;
"Governor, we also have fewer horses and bayonets" -Pres. Barack Obama
I do not consider reversals important, what matters is EPC. I have merchants on my promotion list with upto 70% of reversals, but still their EPC (for me) is better than their competitors who have negligible reversals.
"We are all connected; To each other, biologically. To the earth, chemically. To the rest of the universe atomically." ― Neil deGrasse Tyson