You should consider other houses in the price range, area, square feet, does it fit all your must haves, what can you afford, who is selling it, why they are selling it, how long has it been on the market, etc.
Condition is a major consideration. If it is listed by a Realtor then they should've done a market analysis of the house and priced it according to market values. If you are asking for closing costs to be paid then that is a consideration also. If you have a buyers agency agreement with the agent you are working with then your agent can advise you on what to consider on this particular property.
When your realtor does the comps, dont just look at the raw numbers. Seriously look at the homes those numbers represent and compare updates, features etc - read the marketing comments and the sellers disclosure as well as looking at the pictures. Take note of anything that indicates distressed sale, estate etc and compare those tostatus of the seller you will be negotiating with. Seriously determine if they have priced the home competitively, too high for what the home has in its current condition or they have already lowballed themselves in order to get a faster sale. If they have priced themselves correctly or lowballed themselves DO NOT insult them by lowballing their price.