Request you agent to provide you with all of the recently sold comps for property located in Rohnert Park. This information will provide a "snap shot" of what has been happening in your target location from a SALES perspective.
A review of this information should clarify the locations market activity as well as what your offer price should be.
As what Yasmeen stated, it's a good idea to get comps. In terms of what you should offer, it depends on the situation. First, ask your agent if the listing is a foreclosure, short sale or a regular sale. Then, ask if there are currently any offers. It's all about demand!
For a more detailed explanation to your question on what to offer for regular sales, short sales and foreclosures please go to my blog here on Trulia at the link below!
There are many different homes out on the market - some need a lot of work, some need just a little cosmetic fixing, some are ready to move in. They can all be priced differently. There are also foreclosed properties for sale, short sales, regular sales - this is why you need an experienced Realtor working by your side to help you through the process of buying a home. It could be complicated, but with a good Realtor you can trust it could be really easy!
I recommend asking your Realtor a lot of questions (don't be shy!). When you are actively seeking for a home to purchase, you will learn a lot as far as how much higher or lower you should go on each property you're interested in.
1. How long has it been on the market?
2. How motivated is the seller?
3. What price have other homes sold for in the area in the past 6 mos.?
4. Are there anyone else offering on the property?
5. Is it vacant?
Ask a local realtor to give you comps of the area for the past 6 months: Active, Pending & Sold. It would be good to consider the above factors before offering on a property. Remember: You make money when you buy, not when you sell.