Hi Anh Hoang!
The answers so far are correct. It would be a good idea to interview and work with a Realtor who is not only familiar with your market, but also with negotiating foreclosures.
MOST foreclosures are "AS IS WHERE IS". That means they will not negotiate repairs WHATSOEVER. Knowing what to offer, should it need repairs, deserves expert advise.
Even though most foreclosures will not negotiate repairs, they will usually give you an inspection period by which you can obtain quotes on those repairs. Working with a Realtor will give you easier access to the home to do those inspections.
By the time a foreclosure has hit the market, the bank already is well aware of the need for repairs and notable issues, as reported by their listing agent and/or property inspection reports. So if it is in need of repair, they know to consider that in your offer.
Be reasonable, as they are not interested in the profit margin of others. They don't care how much below market you need to obtain it to repair and make a profit. They care about their "net" or take home pay. It doesn't mean you can't get it at a discount. It just means you can't use your math to understand what they are thinking. That's where expert Real Estate advice will serve you well.
I wish you all the best!