I just ordered some Schmidt Easyflow 9000 refills. I think I'll put them in the higher priced pens to start. Then just play it by ear. I also like the idea of good paper for people to try them out on...not just garbage paper. You can probably tell a difference in the way a pen feels on good paper.
You really can't go wrong with the Schmidt Easyflow 9000 refills. I've been through a few doing journaling and love them. They seem better than the Parker Quink refills. The gel ones from PSI in the clear plastic casing write well, but don't seem to last long. The only "kit cartridges" I've had any problems with or complaints about were the cross style ones.
As for rollerballs, the Schmidt 5888 is considered an upgrade rollerball cartridge, but the 888s are still a great cartridge in my opinion. I really like the Schneider Topball 850s that come with some of the PSI kits and they are surprisingly cheap on Amazon. For what it's worth, the Pilot G2 cartridge has almost a cult following. That, along with the Pilot Precise and Pentel Energel refills, are the same length overall as a rollerball, but they don't have the same tip extension in a lot of kits because of the difference in the "shoulder" design. Technically, they do fit and function in a junior, but just don't look as "natural" as a rollerball cartridge. They fit great in some of the other kits. Also, I recently discovered fineliners (felt tip), but have not tried them yet.
All that being said, you would do well to impress customers with your knowledge of inks and their various uses. Fountain pen and rollerball inks are water based and much more free flowing, so much so that leaving the tip resting on fabric will wick the ink right out of the cartridge. Standard ballpoint cartridges have a paste ink that is solvent based. The solvent evaporates faster than water, thus the ballpoint ink dries faster. Faster drying is better for left handed people. Gel refills such as the Parker Quink, Schmidt Easyflow 9000, and G2 still offer a nice easy flowing ink with a reasonable drying time.
As was noted previously, paper quality makes a difference, but how will they ultimately be using the pen? Writing a memoir, journaling, or just grocery lists? Archival paper? Cotton fiber paper? Cheap paper? Post-It notes? Test some out yourself and maybe have a few types of paper and inks with you for a test drive. Someone might want a regular ballpoint cartridge. Heck, give them 2 if they prefer that ink. You will have plenty of those around once you start putting the nicer ones in anyway. I don't know if you'll have time for that much interaction at shows, but it would certainly build rapport with the customer and trust in your business.
Too much?
