I once translated a series of letters that were written at the beginning of the 20th century. They were sent from Indonesia to Germany, by a German lady working as a missionary.
When I was approached for the job the first thing I did, before anything else, was to ask for sample letters. My client scanned them and sent them to me via .pdf files.
The letters themselves were of a personal nature, so there weren't any technical or legal terms to deal with.
However, they were hand-written, and at times illegible.
So even though the material itself represented no challenge (they were written, after all, in my mother language), I had to invest a lot of time literally deciphering whole passages, and sometimes deducing the meaning of words through context.
When pricing the job I had to obviously take into account the time it would take me not to translate, but to read the original.
My suggestion here is that you NEVER accept a job unless you have seen beforehand what it is about.