Identify the unfair aspect with respect to the sentence extracted from an online Terms of Service:
```
you are only allowed to purchase virtual items from us or our authorised partners through the service , and not in any other way . 

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