It is a grey area but if you apply logic to the situation, any seller who would allow the home to be sold without it being on the open market for a few days is more then likely leaving money on the table. Furthermore no listing agent is going to forfeit the listing commission regardless of when the home is sold. The truth is that the listing agent wants you to use him as a buyers agent, now he may let you know when he has listings available before they go on the market. However just because he does that, doesn’t mean his sellers will accept your offer. Why would they? Conversely if you do make an offer on a home before it hits the market, how do you know that you are not overpaying?
So in my opinion, what your agent said is most likely the truth. Carmel Valley is a very tough market for any buyers. What decent homes come available there, will either be overpriced or receive multiple offers.
You simply need to stay diligent and patient. If you do see something you like you will need to come in very aggressively given the locale you are searching for.