The assessed value of a property, relative to the asking price, is meaningless. The vast majority of taxing entities use something called "mass appraisal", where a computer model is used to determine the value of the properties in a given area of town. It is not unheard of for a taxing entity to actually have a practice of being accurate on their assessments, but it's very, very, very rare. Again, assessed value is meaningless.
That said, what the agent provided you, according to your question, is also meaningless. Go get an agent to represent you and have them put together a market valuation for the property you're interested in. They will pull sold data for similar properties that have sold in the last 6-12 months. Sold data is the most valid determining factor for what a similar property is worth.
Best of luck,