There is a gun store about 25 miles from my house that has a great selection of holsters. I have been there several times to test holsters. I just take my gun with me and show them it is cleared and they let me walk around and try the plastic ones (kydex) not the leather though.
But you can put on the leather, you just can't put the gun in it. Most of the time they will let me adjust the holster pressure.
He's a little more expensive than the internet, but I buy prom him when I can because he provides a good service.
Just like renting a gun before buying one... putting on a holster is a big help in picking the right one.
I put the holster on the see how it fits me, and if I can I put the gun in it and see how it feels getting it out and clear. That's all I can think of to tell you.