If you are at all particular about your choice of printer and are not familiar
with their work, then it is not unusual to ask for some samples, and it is
helpful to be able to describe what type of printing you intend to contract
yourself. This will give you a clear idea of whether the printer can handle
your type of image and what quality level you can expect. You may be asked
to state an intention of what volume level you can afford and the samples
generally should be returned, but the proof is in the printing and any printer
with the mettle to handle your needs will be glad to show you their work.