I had this happen at our local Petsmart here... When Couver was like 5 months old, a lady asked me if I wanted to stud him out to her female and get pick of the litter. At that point, he was too young to be neutered, but I told her heck no.
I think it's important to just educate as many people as possible... Even if you get through to just one person, you've made a difference
