What sort of contractor would reply to this?

[Growernotashower]

I think that job is for HMRC as well!

[Spacecadet]

Sadly there's a reason for that.

The agent/client will then say that they can't find anyone to fill the vacancy, then they'll bring Bob in to do it.

I disagree, the role itself is very low skilled and will just involve a lot of repetitive donkey work for 3 months.
Would probably suit someone with 1 or 2 years experience or a recent graduate

A pro (like me) could get the work done in a month but
either they don't know what they want and don't realise that a decent file loading system can be written, tested and deployed in a month
or they do know what they want and there is no need for a all singing/dancing file loading system but there is a need to have a dedicated contractor on site for the time specified.