The best way to protect your self in this manner is to require the individual to file the complaint under the Digital Millennium Copyright Act. Their notification must contain the following six points of information (this is from an email Lycos sent me when I filed a complaint with them once):
1. A physical or electronic signature of a person authorized to act on behalf of the owner of an exclusive right that is allegedly infringed.
2. Precise identification of the copyrighted work claimed to have been infringed, or, if multiple copyrighted works at a single online site are covered by a single notification, a representative list of such works at that site.
3. Identification of the material that is claimed to be infringing or to be the subject of infringing activity and that is to be removed or access to which is to be disabled, and information reasonably sufficient to permit the service provider to locate the material including exact URL's and references to specific files.
4. Information reasonably sufficient to permit the service provider to contact the complaining party, such as an address, telephone number, and, if available, and electronic mail address at which the complaining party may be contacted.
5. A statement that the complaining party has a good faith belief that use the of the material in the manner complained of is not authorized by the copyright owner, its agent, or the law.
6. A statement that the information in the notification is accurate, and under penalty of perjury, that the complaining party is authorized to act on behalf of the owner of an exclusive right is allegedly infringed.
If a complaint is filed containing the above information, then you must verify the claim (e.g. look at the two web pages), and submit a notification to the offending party that they need to remove the offending content within a specific time frame or file a challenge to the complaint. If they don't reply and don't remove the offending content, then you must remove it yourself. This is the only way to avoid any culpability in any copyright claim.
If there is reasonable evidence of copyright infringement, it is best to get the offending material removed as quickly as possible. If there is any doubt, contact a lawyer. If you don't address the complaint, you can be culpable in any subsequent legal actions. You don't want to mess around with the DMCA, as DMCA violations can carry penalties up to $150,000 per offense.