One of my products has applied for a design patent, and I want to file a complaint against another seller who is selling copies of this product.

Question 1 will affect. If it has been sold, when you apply for a design patent, it is equivalent to an existing design and should not be granted a patent right. Even if it is granted, it can easily be invalidated. Unless the person handling the complaint doesn't understand patents at all.

Question 2, if you can’t get over the hurdles of question 1, there is no need to consider question 2