My work these days tends to be a mixture of both one-off items and the occasional small production run which helps to keep the job interesting and provides plenty of variety. A recent request was a quote for the supply of a large number of tapered hardwood planters. In these situations, where the numbers involved are very high, and the potential financial implication it you get the costings wrong are equally great, I always prefer to minimize the risk and make up a sample first.
As well as allowing you to see whether a design on paper actually works for real, it also gives you the chance to make up any necessary jigs and templates and test them out on the actual project. With the sample completed you are then in a much better position to assess just what is involved as regards time, possible complications and material usage.