If all your questions are answered positively, I would still have a contingency clause in the purchase agreement that would allow you to "walk away" without any penalty that is financial and before I closed I would hire a professional and experienced Inspector that would make you aware of any possible negative/unexpected things that he discovered.I would not buy a single family house for rental unless it was used as a "house hacking" loan that I felt pretty good about qualifying for it.There is only a couple reasons that could make it OK to purchase. 

Are they bitter for some reason? 

If you can get your condo to cash flow there is no reason not to keep it.

It's a cash deal and should be easy and straightforward.Any recos for fast and reasonably-priced attorneys?

For some reason, I have the idea of putting together a detailed binder of my plan, markets I'm eyeing, different number projections and scenarios, etc. and understanding that binder backwards and forwards and pitching the plan to potential lenders.Is there some kind of 'checklist' of documents, figures, etc. that I can refer to in order to make sure I have everything on hand that I might need when addressing lenders' concerns and questions, in order to convince them on my plan?

"Subject to the existing mortgage")I'd probably look into quick claim deed's first and if that isn't possible for some reason look more into the subject to structure. 

They've had too many people have pre-approval letters and when they put in for the actual mortgage, got turned down for various reasons.

This happens a lot in Southern California and Im trying to understand the dynamics.Broker originally represents seller, and ends up representing both buyer and seller,Broker finds a buyer, but broker is only getting %2 commission, would it be reasonable to also represent the buyer.

I would recommend apartment owning over rental hoses for several reasons. 

One user had mentioned Chris McClatchey as being a phenomenal coach/mentor but for a much more reasonable price.