There is more to it than the ratio of other list to sold prices. The asking price has little to do with what is "reasonable." Some sellers are motivated an price at "reasonable" or better. Some sellers want to leave room to negotiate or want more than the market will currently support. You really need to determine "reasonable" based on a CMA of that specific home. As others have advised, your agent will help you with that.
2) The township or city will also have it, some publish it on the tax information on line at their web site and some do not.
A buyer agent can get the data and advice you of the best price to offer and where to stop negotiating.
A real estate agent would be able to provide you with a detailed analysis of comparable sold prices in the neighborhood of a particular listing. This is the same type of comparison analysis that is provided to a potential seller when they are determining an appropriate selling price for their home. Your agent would find several sold properties in the area of a listing and then make adjustments to the sale prices based on differences from the listed property you are considering. For example, adjustments would be made based on differences in square footage, lot size, location, updates, garage size, basement description etc.
The average list price of homes in an area means zip to a buyer, especially in southeastern Michigan. And, if you were also informed to figure the average sale price per square foot of the homes living area, that may also be in error. That's because in southeastern Michigan land, basements, and other factors are not calculated into the area of a home.
Now, agents and appriasers do pay attention to final sale prices. But even those may not give you a good range in value for your bid on a home. That's because sellers frequently give concessions and concession information is only available to real estate professionals. And it is only available on the Multiple Listing Service. Sold prices before concessions are readily available in a home search on Trulia. Simply select sold from the choices.
I agree, working with a Buyer's Agent (which requires signing a contract) would provide the most information about similar recent sales and allow you to make an informed decision. Sample forms are available on the website below.
If you have any other questions, feel free to ask a member privately or post another question on Trulia.