Chris,
This problem interests me as when i need the Rossin done, I will be posting it and the worry about postage, quality of the work and return postage has been weighing on my mind. A worst case scenario for me would be almost exactly what has happened you. The only worse thing would be for the frame getting lost in the post.
Depending on the attitude of the company, it should be evident what you need to do to prove your points. This would be a whole easier if you could bring the frame to them - point out the problems and see what they say. There is obviously a trust issue when dealing by phone and internet and it would be easy for an unscrupulous person to receive an item and then complain to get a reduction in price etc.
From what you say, I would be of the opinion that you should be asking for either -
a full refund OR
the job redone - right
In order to achieve a successful conclusion, you should provide them with evidence - pics etc and i think if you had a credible sprayer locally, some detail from them about the quality etc.
I hope it works out.
On a final point, If you had paid using PayPal (not gift) - would that offer protection? Or would a credit card offer any protection against poor workmanship?
Richard