Before I bought my 850, I had a compression test done at one "neighborhood shop" which showed widely varying results for each cylinder. I then took it to a dealership (that wasn't involved in the sale) for a second opinion. Their test showed much better results. When I took it back to the neighborhood shop for a re-test, the results were better, as well.

So if you have any reason to doubt the accuracy of the compression test (like if they didn't use the most updated equipment to do the test), you may want to get a second test done somewhere else.