I wouldn't want to speculate... :)Is the non-occupying co-borrower a blood and/or marriage relative?

Those people are speculators, and will never beat the returns of true investors who identify where and how they can add value and make solid plans for their investments. 

I also aknowlege that the purchase of both is speculative- the area these are in are always where people want to livePotential disadvantages -- taxes.

I recommend that you either discuss what to cut out of the scope to get to his budget or explain why the proposed rehab scope of work and related costs are appropriate.Again I am only speculating and may be completely off base. 

I am only speculating here, because I have not yet been to the recorder's office to perform the chain of title research yet, but the owner likely paid the property off in full five years ago and did not realize that they were responsible for tax payments on both parcels.Again, what would others do with this tax sale and what would the investment strategies look like on this one?

Not sure if there is anything but appreciation speculation in the SF market.

That way you can make a good decision based on data rather than speculation. 

@Kibby Twong,All the rest aside, buying for appreciation is speculation - read: gambling - it's not investing.You may as well roll the dice on Wall Street.David J Dachtera

It would be hard to sue someon because they "speculated correctly".

We aren't all crazy speculators, I promise.