There's an awful lot of home made shaving soaps available, from all sorts of places and I can't see how to tell the difference, short of trying them all. I've also noticed that people have asked about them a few times here, but nobody has come back and said something is really good - with the exception of Nanny's silly soaps.
Jumping to a massive conclusion I suspect many of these shops are used by women as places to buy inexpensive gifts, and they carry shaving soap for that purpose. Because of that I don't think it's worthwhile risking over the barbershop prices to try soap that may or may not be any good.
And yeah, that's depressingly cynical!