The essence of exploitation and its effects are defined in art. 388 k.c. In the light of this provision, we are dealing with exploitation when one party to the contract, using the compulsory location, infirmity or inexperience of the other party, in exchange for his benefit accepts or reserves to himself or a third party a performance whose value at the time of the contract exceeds in gross the value of its own benefit. In this case, the other party to the contract may demand reduction of its benefit or increase of its due payment, and if both were excessively difficult, it may demand cancellation of the contract. However, this entitlement expires after two years from the date of concluding the contract. This is a convoluted (pre-inclusive) term.
The provisions on extermination concern only reciprocal agreements, that is, those in which both parties commit themselves in such a way that the provision of one of them is to be equivalent to the provision of the other. If the proportion between these benefits is shaken in a gross manner, the person being exploited will be able to demand their change or cancellation of the contract.
A contract for exploitation is not strictly invalid; it is relatively unimportant, or more precisely - repulsive. The exploited entity may, therefore, apply to the court for a change in the amount of benefits, and if it were to be excessively difficult - to annul the contract. The decision changing or canceling the contract is of a constitutive nature. Until its issuance, the contract evokes legal effects expressed in it, as well as those resulting from the Act, from the principles of social coexistence and established customs.
The decision annulling the contract entails the consequence that it becomes invalid from the beginning. If the benefit has been met, it becomes an undue payment, so you can demand its return under the provisions on unjust enrichment.