It depends on the purpose of the CMA. In some cases the home owner intends to get their taxes adjusted. Others are simply curious and FREE is irresistible. Still others go for the annual check up.
Then, there's the one who needs to sell their home. It very likely I've left a few flavors out.
So, how do you sort out the sellers from the rest? If you knew the requesting party was not going to sell this year, would you say, "Give me a call when you are ready to sell your home" or would you do the CMA anyway? Of course, many provide an on-line CMA using on-line data which also has on-line limitations. Most agents will provide these CMA's to everyone who asks. After all, we certainly don't want them believing Zillow or Trulia can provide anything other than a random number.
Having successfully sorted the sellers from the rest, and have that appointment scheduled, you need to focus on what the seller really needs to know. In the overwhelming number of cases they already know what their home is worth and what they are willing to sell it for. So, what do they really want to know? Understanding this is the secret to getting the listing.
Answer those four question EVERY seller has, but don't know they have until you point it out, and you will hit a home run while others are presenting a mind-numbing power point.