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