As a buyer in CA, I have to learn to look up what firearms are legal. It is pretty simple. California DOJ keeps a list. Second, you have to ship to an FFL dealer here in CA and they have the file the paperwork for me at MY expensee so you have a second check to make sure it is legal. I have to pay that FFL $40 to file the paperwork. The seller has very little or no paperwork.
So I haven't heard a good reason not to ship to CA yet. I
I'm the one that has to go through all the extra expense and paperwork, not the seller.
I think a lot of sellers have read the internet lore and haven't bothered to learn the truth.
PS I am a Remington 700 enthusiast. It is pretty easy to figure out that all Remingtons 700s are legal in CA. I was shopping for a youth 22 for my son, they are leagal also.