I won't give out reference checks either generally.
I usually get contacted by one of those companies who are paid to conduct the reference checks, despite telling them each time I will not do the reference checks, they continue to call and act all surprised when I say no.
My biggest issue with them is I don't know whether they are legit, as the employee has either not informed me to expect the call or they have already left the organisation. They claim to have the employees authorisation which they will fax through, however I'm not about to recall a personnel file from the archives to check the signature.
They then try to ask me personnel questions like whether I thought the person was of a good character etc which I'm in no way qualified to answer.
If you aren't using one of these companies, you will have a much better chance if you call the
HR dept direct, and ask them if there was any performance issues with the employee (assuming they have already left). This is the approach I've taken in the past, or have relied on my networks to find out the information that way.