Identify the unfair aspect with respect to the sentence extracted from an online Terms of Service:
```
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 . 

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