IDK what this vendor does if you get a female instead of a male, all vendors should refund. Do they also send an actual male with free shipping? That would be the only useful solution IMO. I just buy 3" fish or larger when needing a male.
As I mentioned in my initial reply, SRC refund once verified that the wrong sex fish was sent. The process for me was 2 days and they were great with communication.
They do not replace the fish at there own expense BUT this is clearly stated in there policies on the website, and should be understood by buyers b4 purchasing. If a person is not ok with that, then buy somewhere else. Pretty simple.
It also states that they do vent every guaranteed fish, but like you say, when smaller than 3” mistakes can be made.
I agree with you that the simplest solution is spend $12 more on a bigger, more easily sexed fish