What can we find out by looking at election campaign expenses in Birmingham?

A Channel 4 investigation has "raised questions over the election expenses of Zac Goldsmith" - in particular only claiming partial expenses on the grounds that 'not all material was used'.

The responses of Goldsmith and the Conservative Party suggest "candidates were justified in only accounting for items used as material can become out of date during a campaign ... the examples raised could be seen in the returns of other candidates."

So let's see if this is true. We have the election expense receipts of Birmingham candidates (Edgbaston here, others to come) - what can we learn from them?