I supervised and coordinated an order for my buyer as his representative in China.
And today i got the email from my buyer. He said as follows:"I have just received this very disappointing reply from XXX – I am beginning to loose my temper, since planning and delivery dates have exceeded far too much – now they also start complaining about the difficulty of painting style Curve. Is there any way you can talk to them and explain to them that delay upon delay are not accepted?"

 If you import from China frequently,you may know delay in delivery happens a lot here.
There are many reasons. But i can list some basic examples here for your reference.

1) the manufactory has many production missions. They need to arrange the production according to their schedule.
2) the factory couldn't manage the production agenda properly. Like they are short of material and need to order from their suppliers
3) the order is not easy to produce due to its high technology and strict requirements then many problems occur in the production.
4) the force majeure or the external factor, like typhoon, on fire, shortage of power.

5) your order for the supplier is not profitable, they let other VIP or profitable orders produce first.

So if the delivery time is very important to you, you need to avoid it when you would like to place the order.

How to avoid the delay in delivery?

Just like what i suggested to my buyer, i wrote follows:

"As i talked to you much earier, you should sign a contract and write all the terms including the delay in delivery and penalty with your supplier. Especially when the 1st order had problem. This will make this supplier to sign the contract with their worked factory and each party will be under the pressures to make things right and properly."

Then he asked me again"If I make contracts with suppliers in future and they are not completed, how do the penalty system work and do I stand any chance of collecting the penalty fine?"

I replied" You are right. Normally, the suppliers won't be happy to accept such term from the buyer. They may refuse it or ignore it. As they knows delay on delivery always happens in China.
So this is a very flexible topic to discuss. I can't tell you what to do exactly.
But you need to consider and dicuss with your suppliers in accordance with the different order and the different situation.
If your supplier inform you the delivery date is 60 days, maybe you can write on the contract like" Maxmium 70 days accepted." Then you can work out the penalty amount on the contract.

I don't suggest you to have particular penalty term with the factories, but you can work out a small penalty amount.

This is just to make the factories feel pressures to follow up the contract strictly. Not really let them punish due to the delay.
If the factory know they never can deleliver on time and the term of penalty is very strict, they will never sign such contract with you. "

At the end of this post, i would like to supplement  that  I do tried my best and use my way to talk to this supplier and they wrote to me and my client that they will advance the delivery 10 days earier and my buyer expressed he accepted and thankness and i think i did my work as his business consultant and representative in China.