I would suggest doing some research, and educating yourself on how pricing and comparisons are done. There's a big difference in how each of the three types of property you mentioned are priced, and the process in which you get ahold of them. An agent can help you out - but I would argue it is irresponsible to rely solely on the agent. You should really have at least an idea of how they come up with these numbers, what they mean, and what the process is.
Needless to say - there is no real answer. It varies from area to area, property to property.
Honestly, there's no set answer to this. What is "realistic" is going to depend on comparable properties in the area, the condition of the home, local market trends, and the seller's motivation... or lack thereof, as sometimes is the case.
This is where have a good agent makes all the difference. If you don't already, find someone who knows the local market. Gina Rosa, who is a fantastic buyer's agent in the Solano area lives and works in Vacaville. She, no doubt, would have the answers you need.
She can be reached at 707.410.7696.
Tell her Carmen said she'd have all the answers. :)