These usually accumulate in the form of late fees and related charges. Patrons may also intentionally accumulate charges by using "premium" services; in an age of increasing budget problems, many libraries have turned to charging either nominal or at-cost fees for services such as ILL, checking out music and movies, or even Internet terminal access.
A child's parent or guardian is liable for the minor's service charges. This can bring up some interesting situations in terms of patron privacy.
Patrons with service charges due totaling over a certain amount will have often have their circulation and/or other rights revoked. In academic libraries, for example, a student with a large service charges balance may be blocked from registering for classes or graduating.
Unlike with the legal safeguards for limits of fraud liability for when someone's credit cards are stolen or they are the victim of identity theft and they are billed for unauthorized charges, many libraries hold patrons liable for all service charges stemming from the use of their library card, especially when its theft is unreported. To avoid such problems, some libraries have launched marketing campaigns to remind users to report stolen library cards. Other libraries have implemented safeguards against the use of stolen library cards, such as by adding users' photographs to the cards.
Libraries may sell their uncollected service charges to collection agencies at a margin. This may make headlines when someone is taken to court by the collection agency, or someone's credit rating is ruined by a collection agency reporting an overdue book fine.
Another popular method libraries employ in attempting to collect anything on old debts is tying it to community service, such as a hunger drive during which each can of food donated yields a dollar of fines forgiven (or a clothing drive, etc.).
Libraries may have in-house loss-control departments charged with reclaiming unreturned items. An episode of Seinfeld featured one such "library cop."
Those with unpaid service charges due to public libraries can find themselves arrested and even jailed for such offenses. Although this also makes splashy headlines, it simply boils down to someone being caught for theft of public property, or for owing the government upaid money.