I'm going to focus on Seller of a hypothetical property you have found and offer that you are going to make. You want to write it so it has a reasonable chance of being accepted. Never offer more than you can afford to pay.
Don't get caught up in idea that you are going to make it work no matter what. Let's face it, some deals just won't work and you have to let them go.
Ultimately, person who gets best deal is person who is least motivated. You have lots of potential homes to purchase... Seller only has one home to sell. Work up numbers.
First, you need to know what current market value of property is.
Do this by going to your title company (you can pick any one you want, just look them up in yellow pages). Title companies have access to comparable sales of homes in neighborhood.
Look for homes that are very similar to one you are preparing to purchase.
Value home you are going to buy based on how it compares to homes that have sold before it. Only use comps that are twelve months old or less.