I can't remember if I read this in 9 Marks or if I've heard Mark say it 99 times, but I seem to recall that Mark's assertion is that if you have the first mark, expositional preaching, in place then you're going to have a greater opportunity for seeing the others take shape over time.  If I'm remembering that correctly, that makes expositional preaching pretty foundational and perhaps "necessary and sufficient" for joining with a body. 

It seems that using the entire list of 9 characteristics as a screen for selecting a church may be to leave off the church reform assumptions that they're written in response to.  Perhaps this is an instance where "beginning with the end in mind" is actually a poor way to start.  Perhaps we should start with looking for evidences of God's grace in a local body, and maybe put a premium on a couple of marks (expositional preaching, sound gospel).  Maybe we labor in love and prayer with the other saints to see the Lord grow the other marks, so that the threshold for joining is significantly lower than 7 of 9 marks or something like that.  Perhaps get the preaching right and the gospel and labor for the rest? 

Here's the other thing I've heard a lot around CHBC.  In the why join a church section of the membership matters class, big emphasis is placed on avoiding a consumer mentality and joining a church as a provider.  There might be a subtle way in which turning the 9 marks into a grid for selecting a church (rather than reforming a church) could feed a consumer mentality and dampen the need to approach every church with a heart to provide.  Our gifts are for the common good, for the edification of the body.  While trying hard to avoid the pride that suggests "we have what this church needs," prospective members should be searching for ways to contribute instead of merely receive.