Identify the unfair aspect with respect to the sentence extracted from an online Terms of Service:
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you understand and agree that you may be required to enter into a separate rental agreement with an advertiser before making a reservation or purchasing a product or service , and such an agreement may place additional restrictions on your reservation , product or service . 

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. OPTIONS: ["Jurisdiction", "None", "Content removal", "Unilateral change", "Contract by using", "Limitation of liability", "Unilateral termination", "Arbitration", "Choice of law"].