Need advise from auction and other investment gurus in Northern CA. Please feel free to correct any of my assumptions below and shed light on the process.

I have been looking at the county tax sales, seems like most CA counties hold these auctions twice a year. What I know so far, that the auctions are all cash, as-is, paid amount is to cover delinquent taxes and if there is anything left the 1st mortgage, all other debt (unless it is a government bill) is written off.  You can get an idea of outstanding assets from paid research sites like prop radar etc.

What I do not know - why do so many of seemingly good properties get "withdrawn" before the auction, do large investors/pros approach the owners and buy them before the auction?

Do you do research on a bunch of them and bid on the ones that are being bid at a reasonable price, to increase your chances of getting one or do you narrow down to just one and go all out ?

Do people also do title search on these? Does that become expensive if you are researching multiple properties?

Would love to hear from someone who has done this Northern CA.