Yes, the dealers I like will in fact not just test a pen but even tune it to fit your personal writing characteristics. I will admit I truly enjoy Nakaya fountain pens. When you order a Nakaya they have a form that you fill out during the process of choosing body and clip or stopper and color and finish that tells the person (there are only two gentlemen tuning nibs) what you like and how you write.
Note there are also areas where you can select "Other" and explain in greater detail how it is you hold your pen and what you will be doing with your pen. I always add that I like my pens moderately wet writers.