If you haven't invested in a vinyl cutter, get one. It will change your life. I bought a 15" cutter (actually cuts about a 10" max,) for $190 last summer and it paid for itself almost immediately. At Christmas time I got the inevitable slew of calls "Is there any way to get one shirt done by Christmas Eve?" that I used to dread, but this time I was glad to do them. I charged $17 each (credit card or Paypal) and put them in packages and tossed them in the mail. About $11 profit for five minutes of work.
Of course, almost all the customers said no need to mail it, they'd "just" come pick it up. But I was able to convince most of them that mail was the only way I do this type of work. The time I save by not having people coming and going helps me to keep my prices as low as possible....
I'm getting off on a bit of a tangent, but customer pick ups are the hugest waste of time for a sole proprietor. It doesn't occur to them that when they stop by (at their convenience) you need to stop whatever it is that you're doing and attend to them. I've even had people tell me that they would come by sometime after they got off work, maybe 7pm...(without even asking whether I planned to be here at 7pm.) Several years ago I adopted the policy that I ship or personally deliver everything I print.
