Check the following as a standard approach to these requests.
Each request should have the following four checks:
Site Collection Admin
Has the request been completed by one of the Site Collection Administrators?
Has the site storage reached the current quota warning limit (NB: All warning limits are 100Mb below the quota limit)?
Does the Site Collection recycle bin contain a large amount of content (i.e. if this was emptied or reviewed would this bring the site back under the current quota warning limit)?
Does the site have uncontrolled versioning switched on in one or more document libraries or lists (i.e. Is the majority of the storage held in versions of files that are likely to be surplus to requirements)?
In addition to the above, check that the Cost Centre Manager approval is attached and the Cost Centre/Project Code is updated.
For all requests I expect to see the answers to the above recorded in the INTERNAL: Notes field as;
Site Collection Admin - Yes
Warning Limit - Yes
Recycle Bin - No
Versioning - No
If any of the items are not answered as expected then the increase should be rejected and the reason why noted in the notes field.