I would only buy a pre-forclosure if:
1- They had sufficient equity to drop the price below current value to give me a great deal.
2- If they had no eqiuty, they at lest had a competent agent or negotiator working with the lender to get my offer accept for less than what is owed on the property (short sale).
Most agents do not have the knowledge or experience to deal with short sales, thus the 10% successful close ratio on a national average. With an offer within 15% of current market value, I can close 80% of the short sales I list.
Again, make sure the 'listing agent' is competent in negotiating. The buyer's agent that claims to be a short sale or preforclosure expert and just shows you homes for sale (not their own listings) always cracks me up. The listing agent is the one that needs to be the expert, the buyer's agent sits back and waits for the deal to get accepted.
Happy house hunting.