The objective of this thesis was to find out how the law differs in trader and consumer installment purchase contracts and when traders or consumers make contracts themselves. The law of installment purchase applies when both sides are traders or consumers, and consumer protection act must be applied when a trader offers commodities to consumer. This thesis has been done from the commissioner’s point of view, therefore, it was focused especially on the object’s repossession and statement of account.

The theoretical part of this work consists of installment purchase and of its related rules, and of enforcement office and its duties. As research method, a qualitative research method has been used. The work was done as a desk study, along with observation based on the author’s own experiences. Laws, preparation documents, cases, minutes of executive assistance and statements of account and the office’s own instruction materials have been used as sources of research.

Differences between the law of installment purchase and the consumer protection act are based on EU consumer protection directives and universal consumers’ rights. Consumer protection act is obligatory and cannot be disregarded even by contracts to the consumer’s harm. The contract of installment payment details have been specified strictly in both laws. If the contract is not lawful, it is harmful to the seller.

The study can be considered reliable, since it is mainly based on current existing laws and other reliable sources.