I have a short version, and a long version with explaination:
1. Short version - call up agents and be upfront and say you are just looking for information, not a meeting at this point in time, and ask if they wouldn't mind giving you some free information on home sales in your particular area. If they say ok, then there you go. If they want to set an appointment, say thanks but no thanks.
You could also call the public tax records office and if you have the addresses of the homes you are interested in, they can usually mail, email or fax you the sale information.
That office contact information is:
Stafford County Commissioner of the Revenue
P.O. Box 98
Stafford, VA 22555
Office Hours: Monday - Friday, 8:00am - 4:30pm
Phone: (540) 658-4132 FAX: (540) 658-4120
2. Long version-
The most reliable source is the information from MRIS (which also links up to tax info), metropolitan regional information system. It is the system that the agents in Stafford county use to input the sold information. (MRIS goes as far south as Caroline county, and also covers DC and Maryland)
Agents pay quarterly fees to access this system as members to be able to input information for all other agents to access. MRIS then turns around and sells this information to other 3rd party sites such as zillow.com, realtor.com and of course trulia.com.... which then charges the agents to become 'featured agents' ... so really agents pay to put in the information in a big pot, the owners of the big pot sell the information to other companies, who then charge the agents to get leads from their sites. So really all the information is connected to the agents in some way.
The good news is, all agents aren't sleezebags and crooks. Many, hopefully even most, are actually interested in helping people like you find the answers they need. The idea is if they help you enough for free, when it comes time to buy or sell and you need some professional help, you will consider using their service so they can make some money. Even if you don't, maybe you will remember how nice and helpful they were when you know of someone else who needs help.
A quick and informative CMA for a particular are (say 2-3 mile radius of your home) of recent sales could take a good agent as few as 5 minutes of actual work. So they really shouldn't have much problem with helping you.
I hope this was useful information
Good luck with your sell and purchase