Always get a deposit of at least 50%, even if there isn't anything unusual about the pens and you believe you can sell them anyway.
While I agree that getting a deposit is a good idea for making several pens just for a customer, I would not make a blanket policy in asking a
repeat customer for an advance. I would let the frequency of the repeat business dictate how I treated a deposit or lack thereof! I've had repeat customers who spent hundreds of dollars on pens and asking them to put up a deposit now would be an insult in my eyes.
The only exception would be if the customer asked for a very unique pen using rare or odd materials that I might not be able to sell if he changed his mind.
I'd give it some time. I had an attorney in Wyoming email me a custom pen order after ordering three others from my website. I finished the pen and emailed him but got no reply, a few more emails went unanswered as well. A few weeks later he emailed asking how I was coming along with the pen! I called him and it seemed that my earlier emails were going into his "Spam" folder and he never saw them.
Never assume emails are 100% failproof!