Hi Albee,
You cannot buy a house based on previous history. This is wrong wrong wrong.
If previous owner got rich by staying in that house and sells to you, and if you think that it wil bring you the same "wealth luck", you might be in for a disappointment. When occupants change, the Feng Shui of the house may or may not remain the same. We have ways to determine that of course.
On the other hand, if the previous owners goes bankrupt, there is still a likelihood that after you buy and stay in it, it will bring you good career luck. I personally have found houses for clients that previous onwer goes bankrupt (and they grab the unit at good price) , but after shifting in, they are doing very well!.
So Feng Shui is not simple. I will advise not to DIY in this aspect and don't buy a house based on past history...it is not accurate.
For your qns:
1. new condo in good central location : owner has not move in yet but has to sell the house due to unable to service bank loan cause by speculating on property on wrong timing (economy crisis) Price : $1.2 Mil drop to $1 mil
--> if the owner havent even stay in the house yet, that house feng shui is not affecting him. It is his current house feng shui that is affecting him. Where you stay will affect you (even in hotels!). If you own a property and don't stay in it, it will not affect you in any way.
Furthermore, i am very sure that guy must be in bad luck period in his Bazi luck cycle. A person in bad luck always do the wrong thing at the wrong time!
2. new semi detached house in rural area: Developer has to put up for auction due to cash flow problem and bankruptcy (economy crisis). Price : $2.4 Mil drop to $1.4 Mil
--> I guess you know the answer by now after my explanation above