I experienced the exact same problem. After careful geometry data collection and several test rides of bikes I already knew wouldn't fit, I came to a conclusion about what I believed would work for me. I offered a $200 non-refundable deposit on the bike I wanted ordered with the understanding that I believed the bike would work for me, but if once delivered and assembled I decided it just wasn't going to work, I'd walk away from the deal and lose the $200. I was confident about what I wanted, but wasn't willing to commit to a deal on a bike I never even saw in real life. My offer of a large deposit assured the shop they wouldn't get killed on an un-sellable dust collector taking up room on the floor.
In the end, everything worked out beautifully but I did a ton of homework, test rides and research (and hand wringing) while everything came together.
-Kedosto