Local investment clubs and events that are not trying to sell you something.  

Is it ethical to place an offer on B and only cancel A in the event that B accepts?

., 506(b) and 506(c)) exemptions, where a disqualifying event occurs following the effective date of 506(d).

This should be a fairly simple question for a local RE attorney to answer, if you give them an accurate account of events.

One event will be held in your state I am attending the one in NYC as that is where I am from.

They can call your servicer up, which can initiate a chain of events which will get your mortgage  "called", which is finance jargon, for "pay me my money now because you broke our contract".

Inadvertent ponzi schemes are more common with funds than they are with one-off syndications and they generally occur because the promoter fails to keep their books in order properly.  

As my luck would have it, a month after closing on one of them, the husband & wife had an "event" that landed the Mr. in jail.  

the difficulty selling one property in the future did not occur to me

Not myself, but there are a lot of people out there that treat these scenarios as "risk vs reward" events and skirt the grey areas.