Post around to some of the more popular bulletin boards...with Carfax, you can check one record for ~$20 or buy a full month of unlimited checks for ~$25. A some people will check for you on their unlimited account. I would do it, but mine has expired.
I guess you could also purchase the report and I believe they offer a money back guarantee if not satisfied...you could always find something to not be satisfied about...although it's probably more trouble to get a refund than it is worth.
Lastly, remember that with all these services, "Absence of evidence is not evidence of absence" ...just because the carfax report is clean, dosen't mean the vehicle hasn't been in a serious wreck. It could mean that it just wasn't reported.