That happened to me a couple years ago. I messaged a guy on eBay out some flat tappet Ford lifters to make sure they had the hardened feet on them.
After realizing there's a difference, he told me yes, then raised the price from $18 per 4, to $350 a set. And added ''these are the hardened lifters, I know what I have'' in the description. Suddenly it became cheaper to go roller, so that's what I did.
Over a year later, he still was paying $.65 a month to list the lifters he can't sell.