Car insurance quotes are not "fixed in stone." They are estimates subject to verification and adjustment by the car insurance company. Primarily the information provided by a potential applicant is the basis for calculating the car insurance quote. The actual policy price issued (supplied) by the insurance company sometimes does not match the quoted price.
The auto insurance industry is regulated at the state level (as opposed to federal). Each insurance company's rates and underwriting rules are filed with and approved by the responding state. Due to these regulations, insurance companies must issue policy premium (price) accordingly. They are not at liberty to adjust premium when the quoted price does not match the actual policy after verification of applicant information.
Motor Vehicle Records (MVR), Claims Loss Underwriting Exchange reports (CLUE), insurance scores from credit reporting agencies are usually obtained and are factored into the rate at time of quote. Sometimes technical issues prevent reports from being generated or they are simply unavailable due to Web site maintenance. However, prior to a policy being issued this information will be retrieved and the quoted price will be adjusted if necessary.
Other information is not as readily verified. Prior insurance, driving school, good student grades, and other discounts are generally verified by submitting paper documentation. These documents are rarely available during the quoting process and often are not submitted with the application. Insurance companies will request the information to follow the application in a reasonable amount of time and will remove discounts, raising premium, if not received.
Once a policy is issued, and coverage begins, the premium due will reflect the state approved rate. If the quoted price was inaccurate the policyholder is still responsible for the actual premium for the time insured. This system is seemingly unfair but is actually for the protection of the insurance consumer. The ultimate rate charged for a policy is that which has been reviewed and approved by the regulating authority. Insurance companies are not allowed to "make it up" as they go along. A "bait and switch" tactic which charges customers a low rate at the start only to be raised during the policy period for no legitimate reason is illegal.
Shopping well in advance of an expiring policy will greatly diminish the chance of a premium adjustment after a policy has been issued. Policyholders who do experience an up-rate can cancel their policy and go elsewhere. Any unused portion of premium after cancellation will be returned, without penalty, to the policyholder.