Everyone wants a bargain! But understand that it depends on the local market and other factors (i.e., city, neighborhood, economy, condition of the property). Sacramento has lots of bank-owned. 30% below is not bad; it's probably standard.
I know because our company has bank-owned listings in Sacramento. I also know the Sacramento market. Anyway, I hope that helps.
I see you're in Fremont. Some areas of Fremont, people have bought 50% below market, but Fremont is bouncing back and inventory is low. It really depends on the local neighborhood, economy, condition of the property, etc..
When I attended auctions, I've witnessed properties selling at 50+% below market, particularly in Discovery Bay and Antioch. Also, you should make sure that the values you are looking at are true values. A real estate agent who is well-versed in this area should be able to tell you when looking at a street if that is a good value.