CPO comes up here on the ol'JukeBox every week or so. Just Fyi & fwiw, the lists of what's covered and not covered via BMW's boilerplate:
BMW Certified Pre-Owned - Warranty - Covered - BMW North America
Not covered is the next tab on that link...all subject to some interpretation by your friendly, or not so friendly dlr.
CPO Inspection guidelines can easily be found on web, eg a quick Yahoo search,
with links of the pdf inspection list(s).
From reading here on the Board, some dlrs obviously follow the rec's, and some give it a wash/wax by the $8 an hour kid, and sell it as 'CPO'.
CPO inspection guidelines - Yahoo! Search Results
Whether one feels more comfortable with the CPO net, and thus the usual extra cost built in, is up to the buyer.
GL, mD