The developer declared bankruptcy.

Sometimes homeowners are forced into bankruptcy.

People go bankrupt because they take risks beyond their means and I agree we have a cycle of bankruptcies on the way in the near future!

That plan has never ended in bankruptcy/foreclosure for anyone ever...

Gutsiest thing I've done is JUMP back into real estate even after losing everything.And I've acquired over 1,000 apartment units ever since.Here's my story (so you see how bad it became and how I rose from it all):Part 1 - https://www.biggerpockets.com/forums/55/topics/690349-from-bankruptcy-to-1-000-units-part-1-thru-the-dark-tunnelPart 2 - https://www.biggerpockets.com/forums/55/topics/692382-from-bankruptcy-to-1-000-units-part-2-rising-from-the-ruinsPart 3 - https://www.biggerpockets.com/forums/48/topics/695243-from-bankruptcy-to-1-000-units-part-3-how-to-build-an-empire

Or they might just file for bankruptcy and not pay anything and create a new HOA.

For example pre-foreclosure leads have been around for a long time as foreclosure is an indicator that the property will soon be for sale.Vacant property leads indicate that the owner has already left the property.A newish source is HOA liens which is an indicator that there is a financial issue associated with the property.Unpaid property taxes are a similar source.Bankruptcy records are an interesting lead source as you can see when properties may be losing bankruptcy protection.Several "I buy your house for cash" sites sell leads.There are several others sources but that gives you an idea.So basically you are putting a marketing plan in place and contacting owners at the opportune time.

I've rented to people with bad credit who I believed would be good tenants and were, a couple who had a medical expense bankruptcy for one.

You pay tons of money, getting in debt, it keeps you the hook forever because you can't file bankruptcy on student debts.

If you want to avoid some of that, the person needs to do plan their estate.I know very little about German law except what I learned about its old bankruptcy law (which was crazy).