Hi Jay,
As far as avoiding this problem in future, i agree with all those who have mentioned revising your trading terms.
Just be aware that if they are on your invoice only, they may not be enforceable because they may not be disclosed at the time of entering into the agreement.
There should definitely be provisions to cover you in the event of the client changing their brief, and might i suggest something along the lines of a time limit after delivery for them to notify you of any defects.
If you would like a hand, please visit
www.nbservices.com.au and send me your details via the contact us page.
I'm happy to have a chat about other options you could include as well.
Regards
Paul