Checking past prices yourself is more reliable than asking a real estate agents to find their own subjective "comps." Real estate agents only get paid when a transaction takes place; even a big swing in price that mean a lot to you (as buyer or seller) means very little to the size of an agent's commission. This means that - paradoxically - a buyers agent has an inherent bias toward encouraging buyers to make the highest possible offer and a seller's agent has an inherent bias toward accepting the lowest possible offer.
This doesn't mean agents are bad people, just that they are motivated by self-interest just like everyone else and so consciously or unconsciously find comp prices that reinforce that bias, and you should always find independent price information rather than relying on your real estate agent for everything. "Trust but verify" applies to your real estate agent same as it would to a used car dealer or anyone else.
A real estate professional can give you access to this, along with a number of other critical factors in addition to previous-sale info. At this particular time in the market it pays to know "everything" about a property; as you do this it will become known which individual, or combination of factors, properly determine the value of a home. Cheers,
which is the DC government site. It is generally up to date and easy to use. If you need more information or details about past sales, feel free to email me at firstname.lastname@example.org